Batteries are at the heart of all our radio control systems and they represent a single, often fatal, point of failure. Hence, they deserve the best treatment we can give them.

I dare say much of this information has been published before, in one form or another. However, there is no harm in repeating what we should do to look after them.

I have spend about 25 years as an electronics/electrical engineer of which a reasonable proportion was spend designing battery charging systems and so I am sometimes called upon to pontificate about battery related issues in my club. It has been suggested that it would be useful to share these thoughts with a wider audience, which is what I am attempting to do here. My direct experience encompasses designing commercial & military chargers for both lead acid and NiCds, including various fast chargers. I have also spent many hours researching ‘memory effect’, which in my opinion has much in common with the Loch Ness Monster! I only recently started working with Lithium batteries so I will confine myself to NiCd, NiMH and lead-acid types for now. Drop back for updates on Lithium in due course. (I will try an update it under 25 years though!)

One word of warning – if you supply NiCd battery cyclers, don’t read this – you won’t like it!

What is a battery?

Simply put a battery is a store of chemicals that when allowed to react under controlled conditions produce the electrical charge. The ‘capacity’ of the battery is simply a measure of how much charge it can generate. Eventually all the chemicals are converted, and no more charge can be drawn from the battery; it is flat. Fortunately, the rechargeable types allow those chemical reactions to be reversed and electricity converts the chemicals back to a state where they can release the charge again. Due to the nature of the chemical reactions how we get the charge back into the battery is critical to correct operation of the battery.

Before I continue, “rabbiting” on about charge, and start on about current and voltage let me offer a simple analogy that will (hopefully) allow those with out a working knowledge of electrickery understand some of these concepts.

Consider ‘charge’ to be the amount of water in a bucket (the battery). If that water starts to flow out, the speed at which it flows is the ‘current’. The greater the speed (larger the current) the quicker the bucket is empty (battery flat). The force driving the current is the pressure of the water; this is ‘voltage’ in electrical terms. A higher pressure will cause the flow to be larger (a higher voltage will give a bigger current) all other things being equal. If the water is flowing out of a hole in the bottom of the bucket, the bigger the hole the less pressure it takes to drive out a given flow. The size of the hole is a measure of its resistance to the flow; again, this is analogous to electrical resistance. A bucket of water emptying through a hole is similar to a battery discharging into a ‘load’ (a load is anything the battery is supplying current to). As the water level drops, the pressure falls and the current slows. The bigger the hole, the higher the pressure, the quicker this happens. With a battery as it discharges the voltage drops, the current falls, until eventually, there is no voltage and no current. The bigger current, the higher the voltage, the quicker this happens. Now that is about as far as I can push this analogy, but I will keep come back to it as required.

Battery Types

In general, we use two different types of battery, the “Lead Acid” and the “NiCd/NiMH” (note I know NiCd and NiMH are different but they have very similar handling requirements).

Recently Lithuim batteries have become widely avaiable and popular with the electric plane jockeys. As I said earlier I have only just started working with Lithium batteries yet, and so I will not pontificate on those at this time.

I will briefly describe the basic types of Lead Acid and NiCd/NiH batteries and what they are used for.

In practice, we cannot change the way we discharge our batteries, they are connected to the radio, glow plug or whatever and they discharge! The bit we are in “charge” of is charging them. The two main types NiCd/NiMH and Lead Acid need two different methods charging. I will describe these in detail as it is worth understanding the differences.

Types of Lead Acid

Lead acid batteries will be your 12V flight box battery and the ‘car battery’ you use for charging the flight batteries of an electric powered model. The standard 12V “car” battery comes in two basic types; starting (cranking), and deep cycle (marine/golf cart). The starting battery is designed to deliver quick bursts of current (such as starting engines) and have a greater plate count. The deep cycle battery has less instant current but can sustain long-term delivery. Starting batteries should not be used for deep cycle applications and visa versa. The so-called Dual Purpose Battery is only a compromise between the two types of batteries.

These then come in two types of construction the ‘wet cell’ and the ‘gel cell’. At this point, I will stop with the boring details but just say that in generally, the small 7Ahr flight box battery, the Cyclone cell and the more expensive batteries will be ‘gel’ type. This means that the liquid (the electrolyte) in the battery has been treated to make it like a jelly, so that it doesn’t spill, even if the battery case is punctured.

Gel Battery  Cut away

Click to enlarge

Wet cells are self-evident, the electrolyte is completely liquid. As this liquid is a strong hydrochloric acid it is not a good idea to spill it! It also has a tendency to evaporate and requires topping up with deionised water regularly.

Wet Battery Cut away

Click to enlarge

General-purpose car batteries that are sold as maintenance free or sealed are not always gel batteries. They will be what they say on the tin – sealed, but the electrolyte may still be liquid inside. These are less safe for general transport than gel types, but are a lot cheaper. I would always choose a gel type when I can afford to.

For field charging of flight batteries, choose a deep cycle battery, sometimes called a ‘Leisure Battery’.

2V Cyclone cell

There are also small cylindrical 2V Cyclone lead acid batteries, which are unique (even though they are based on lead acid chemistry). I use one of these in my flight box for the glow plug power source. As they are significantly different, I have written a separate section on them.

Charging Lead Acid Batteries

All lead acid batteries have to be charged at a constant voltage.

This means that the voltage is maintained at a fixed level by the charger (fixed pressure) and as the battery charges (the bucket fills up) the current will drop (water flow rate) from an initial high value to virtually zero.

Now to complicate things; in simple terms there are two charging methods referred to as ‘float charge’ and ‘cyclic charge’. The exact value of the fixed charging voltage determines which of these methods is applied.

Float Charger

This refers to a charger that can be left connected indefinitely to the battery with out damaging it. In theory, the battery never reaches 100% charge on this voltage (unless left for an infinite time). In practice, it should recharge from ‘normal’ use overnight, say 16 hours. However if the battery is completely flat before charging it may never recover on a float charger. These are often referred to as trickle chargers, but that term has been incorrectly applied to low rate cyclic chargers (below) in the past.

Cyclic Charger

This refers to a charger that can bring a battery to full charge in a short time, generally about 8 hours. However if left connected it will go on to damage the battery by ‘over charging’. The time it takes to bring a battery to full charge will be a function of its output current in relation to the battery capacity. In some cases, particularly certain makes of gel batteries, the minimum charge time is controlled by the battery chemistry and cannot not be shortened not matter how much current the charger can put out. At the other extreme wet cells can be recharged very quickly, but at the risk of causing an explosion if you get it ‘little bit wrong’!!

The good news is that most modern chargers automatically switch between these two modes of operation. They start with a higher output voltage in cyclic mode. When the charge current falls below a preset value the voltage is lowered to the float charge value.

So far so good. Now comes the difficult bit – different types (gel or wet) require different charging voltages, particularly for the float charge mode. Gel types must be charged at a float voltage of between 12.9-13.4V for a nominal 12V battery (depends on manufacture, temperature etc), while a wet type is quite happy with 14V across it. This would be a very rapid cyclic charge for a gel battery, and if left on would soon damage it.

It is essential therefore when buying/using a charger that it is designed for the type of battery you are using. In particular, always ensure that the charger is designed for gel types. You will not harm a wet battery charging it with a gel charger (it may simply take a bit longer to charge) but the reverse is not true. Again, most modern charges are designed for gel types or have a switch on them for selecting the battery type.

Charging Voltages

For those with the means to check their chargers the voltages for the various modes and battery types are given below. You will need a good digital meter to distinguish between these values.

From the above you will (I hope) have worked out that it is important to ensure the charger used is suitable for the battery you are charging. Many modern chargers include these options, but if you are using a gel battery ensure that they state suitable for gel batteries, not just maintenance free batteries.

A suitable unit would be the Draper 12v Intelligent Battery Charger, which as a RRP of about £40, but can be obtained for as little as £30 if you shop around. (2005 prices)

If you are only charging, a small 7Ahr flight box battery the Clarke 12V Trickle charger is ideal. This is a small plug in unit and is available from Argos at £10. Similar trickle chargers for this type of battery can be obtained from model shops, when you buy the battery.

These can also be connected permanently to a larger battery that you won’t be using for weeks or months, to keep it in good condition.

Lead Acid Battery Care

Looked after properly lead acid batteries can last for years, a lot longer than the 5-year warranty you get on most car batteries. However, most don’t survive that long and the battery manufactures love us for it! The statistics for batteries fitted to cars are something like only 30% of batteries sold today reach the 48-month mark.

The single biggest cause of failure, in fact 80%, is related to sulphation build-up. This build up occurs when the sulphur molecules in the electrolyte (battery acid) become so deeply discharged that they begin to coat the battery's lead plates. Before long the plates become so coated that the battery dies. The causes of sulphation are numerous.

Let me list some for you.

* Batteries sit too long between charges. As little as 24 hours in hot weather and several days in cooler weather.

* Battery is stored without some type of energy input.

* "Deep cycling" a battery not designed for it.

* Undercharging of a battery, to charge a battery (lets say) to 90% of capacity will allow sulphation of the battery using the 10% of battery chemistry not reactivated by the incomplete charging cycle.

* Heat in excess of 100°F (38°C) increases internal discharge. As temperatures increase so does internal discharge. (Not normally a problem in the UK)

* Low electrolyte level - battery plates exposed to air will immediately sulphate (only applies to wet cells of course).

* Incorrect charging levels and settings. Most cheap battery chargers can do more harm than good. See the section on battery charging.

* Cold weather is also hard on the battery. The chemistry does not make the same amount of energy as a warm battery. A deeply discharged battery can freeze solid in sub zero weather.

Not all of these apply to our situation. The most common cause of failure with our batteries will be deep discharge followed by sitting too long with out a charge, probably in the cold as well.

You know the situation; you have been trying to start a reluctant engine at the field. Eventually the flight box battery dies, but you ‘keep’ trying just in case the engine kicks into life one more time (fat chance), until the battery won’t even light a torch bulb. Then you stomp off home, leave the flight box in the shed for a week or more, while the temperature drops during the unexpected cold snap. Then you think about going flying so you wack the charger on the battery and give it a quick charge before you go up the field again.  Guess what ……. you have just committed ‘batterycide’, you have killed your poor old flight box battery, that never did anybody any harm and just wanted to try its best to start your engine for you, you heartless swine!

So the ‘moral’ of this story is:

* Use a good battery charger that is suitable for your battery type and capacity

* Use a charger that has automatic float charge change over (or be prepared to take it off charge at the right time)

* Do not leave a lead acid battery discharged, in fact charge it up as soon as you return from the field

* If possible, do not expose to extreme temperatures, less than 0°C or more than 38°C.

Cyclon Batteries

You may not have heard of these but they are excellent for using as a glow plug battery. I prefer a separate battery for the glow plug, rather than the more common arrangement of having a 1.5-2V source derived from the 12V flight box battery. With two separate batteries you can at least attempt to flick start the engine if the 12V battery is flat. They can also be used for on board glow systems, but are heavier than an equivalent capacity NiCd/NiMH battery.

Cyclon batteries are lead acids, therefore they are best charged at constant voltage. The voltage range is between 2.3-2.4V and 2.4-2.55V. The lower voltage is the 'float' charge voltage and the cell can be left connected to this indefinitely. The higher voltage is the 'cyclic' charge voltage and the cell should be disconnected from this when it is charged. End of charge is indicated when the current drops to less than C/20, in the case of a 2.5A/hr that is less than 125mA.

Unfortunately, I have yet to find a supplier of suitable chargers; I have always constructed my own. The manufacture’s data sheet says that they can also be charged at a constant current. However, in 20 years I have not found a data sheet with the value of that current!

For general modelling use, I use a 2.4V constant voltage charger. I generally only connect this to the cell every third session, but that depends on how long you leave the cell connected to the glow. I let it charge for about 8 hrs maximum. 2.4V is safe for this as it is still in the float charge region.

The Cyclon is better than other lead acids for long-term storage and can be left for about 12 months between charges if fully charged to start with. If it is not going to be used for long periods, then connect to a float charger at 2.3V or top it up regularly. The manufacture gives it a 15-year life, and I can vouch for that so far!

NiCd/NiMH Batteries

I am going to discuss these batteries types as if they are the same and to save typing call them NiXX. The purists out there will now be howling into their cornflakes “oh no they are not – they’re different you philistine”. However, for most practical purposes as far as we are concerned they are essentially the same. Where there are specific differences, I will highlight them.

NiXX batteries now come in a bewildering variety of types, capacities, capabilities and can be made up into packs of any number of cells, which means different voltages. Therefore, I will talk about ‘voltages per cell’ where relevant. Charge currents will be quoted as a fraction of the cell (pack) capacity.

So for example if I have a 4 cell 1000mAh NiXX receiver pack it will have a total voltage of 4 x 1.2V = 4.8V as each cell will generate 1.2V nominal. It will be charged at a rate of C/10 for a slow charge over about 15 hours. C in this case is 1000mAh so the charge current will be 100mA. (1mA = 1/1000 Amp).

A typical 4.8V 1000mAh receiver batterey pack is shown opposite. These days I exclusively use 5 cell packs, with 6.0V nominal voltage. These give a 'crisper' servo response. The current darin will be higher (you get nothing for free!) and so I go for 1500-2000mAh packs. Make sure the reciever and servos are rated for 6.0V; most are but some aren't.

Charging NiCd/NiMH Batteries

All NiXX batteries must be charged at a constant current. It is extremely dangerous to do otherwise.

In terms of our water analogy, this means that water is fed into the bucket at a constant rate through the hole in the bottom. As the water rises in the bucket, we need to increase the pressure (voltage) to ensure the flow remains constant.

As with lead acid batteries there are two basic charging methods, both constant current, depending on how much current is used relative to the cell capacity. The actual rates are not precisely defined so I will use my own definitions as described below.

Slow Charging

Slow charging is a rate of C/10 and will charge a flat battery in 14-16 hours. Therefore, in the case of a 1000mA pack this will be 100mA. It is a relatively safe charge rate and the battery can be left connected for long periods without damage. However, contrary to some peoples beliefs, not indefinitely. Even slower rates can be used without problems, just extend the charge time accordingly.

Fast Charging

I will use this phrase for charging at a rate of 1xC or faster. So this time our standard 1000mA pack will be charged at 1000mA or 1.0A. At these high currents, the batteries will get hot and the potential for overcharging, with disastrous consequences, is very high. Batteries must never be left on a fast charge with out some method of automatic cut-off.

NiCD/NiMH Battery Chargers

Slow Chargers

All equipment that is sold with NiXX batteries in will be supplied with a suitable battery charger (unless anybody knows different!). If we restrict the discussion to radio control equipment then these are invariably slow chargers for the receiver and transmitter batteries. The choice is then simple:

* Use the charger supplied in accordance with the manufactures instructions. They are safe to use, won’t harm the batteries and reliable (because they are very simple).

* Use a third party charger in particular a fast charger

The main limitation with the slow chargers provided is that you can’t quickly charge the batteries if there is a last minute change of plans, the weather improves or the wife says “why don’t you go flying instead of coming shopping with me?” (Yes I know that these are rare events but they do happen occasionally!) A third party fast charger goes some way towards eliminating this problem.

Fast Chargers

These days the choice of fast chargers is HUGE. I suppose most are designed for charging flight packs in electric powered models, but others are very useful for charging radio system batteries. With out exception that I know of, they all use the same technique for determining when to terminate the high current charge, called peak detection.  This is a reliable method and ensures that near maximum charge is put in each time, regardless of the state of discharge at the start.

As there are so many options for choosing a fast charger, I will only highlight the main features and possible problems. Peak detection relies on they fact that when fast charging the voltage of the battery rises continuously, until at ‘full charge’ it drops slightly. This is the ‘peak’ that the electronics detects, and terminates the fast charge. Again, in all of the cases I know, the charger then changes the current to the equivalent of a slow charge.

This graph taken from the data sheet for a Sanyo 4AHr 5-cell NiCd pack clearly shows this peak for a 1.5C charge current of 6.0A. (The different lines are for charging at various ambient temperatures).

At this point NiCd and NiMH deviate in their characteristics. NiMH may not fast charge as fast as NiCd; typically, manufactures will only specify a fast charge for NiMH as 0.75C maximum. Therefore, a 4AHr NiMH can only be ‘fast’ charged at 3A, and will take 1.5hours, which falls outside my definition of ‘fast charge’!

To complicate things further the ‘bump’ in the charge curve for NiMH is far less pronounced than in NiCd and temperature dependent. Therefore, the electronics have to be more sensitive to detect the smaller change. Ideally, they will detect that the ‘rate of change’ falls to zero, rather than look for a drop from a peak.  Technically terminating the charge after the peak is a slight overcharge, so the more sophisticated ‘slope change’ detection is a safer option as well.

DO NOT assume that all fast chargers are suitable for NiCd and NiMH, check the manufactures data. If it doesn’t say ‘Suitable for NiMH’ it isn’t.

DO NOT charge NiMH faster than 0.75C unless you have checked that the manufacture allows this.

That said I know that NiMH are now used extensively for power packs and given very fast charges as a result. Just be warned that not all NiMH are equal in this respect.

A couple of years ago I bought a Mainlink 6 channel charger for my radio batteries, transmitters and receivers. I have taken to using 5 cell NiMH receiver packs with high capacities of 1500mAhr+ to power modern digital servos. Consequently, a multi bank fast charger with good peak detection was virtually essential. I consider building my own or adapting a ‘spare’ unit from my stock of old military chargers, but decided it was far easier to buy a purpose designed unit.  (I’m getting lazy in my old age).

The Mainlink Delta 6 unit has been an excellent investment. The illustration shows the latest incarnation of that product.

NiCd/NiMH Battery Life

As with all things, looked after properly, NiXX batteries will last for years. They do ‘wear out’ and there is a limit to the number of charge/discharge cycles that they can tolerate, manufactures typically quote 300-500 cycles. However, these are FULL charge/discharge cycles and normally at high currents of 1xC or more. The batteries in our radio system can reasonably be expected to last far longer, probably for 1000’s of part discharge cycles. Even if its only 500 cycles that’s many years for your average weekend only flier.

This does not apply to batteries used for flight packs, because you guys really do ‘cane’ these, with 10C discharges and 3-4C charges, until they get hot enough to fry eggs! (Poor little batteries). I confess to having no significant experience of electric flight (tried it and got tired of waiting to recharge the flight pack!) and the stresses it puts on batteries. Even the military systems I have worked on don’t punish batteries as much as that. Therefore, you will need to draw your own conclusions about the expected life of flight batteries. At least if they die unexpectedly the model can glide home (unless you are using BEC of course – oops!)

The failure mode of NiCd cells that you cannot do much about is “separator deterioration”. This will occur in all NiCd batteries as they age. The separator breaks down allowing the plates (electrodes) to touch and short out the battery. Millions of testing hours on thousands of cells has established the mean time to failure (MTTF) of a single cell to be 8 years for cells/batteries maintained at 25°C. Due to the random nature of the failure mode, this means a four-cell receiver pack has an MTTF of 5.7 years, while an eight-cell transmitter pack drops to 4.8 years.

Does this mean that you should automatically replace your batteries at say 5 years and 4 years? Not really, as separator failure is not a catastrophic failure and can be detected. It manifests itself as a higher self-discharge rate. This is the tendency of the battery to discharge when not connected to anything i.e. switched off for our RC equipment.

Transmitters always have a battery meter, and you can get cheap monitors for your receiver batteries. These are not a very accurate (due to the nature of the batteries, not the integrity of the meter) but they will give you a guide. Charge the batteries to capacity and the monitor the battery voltage over a few days to a week by turning the system on briefly. If it drops significantly, say 15% in a week it is on its way out. If it drops 10% in a day, it is ballast – ditch it before it ditches your model!

I would recommend that you purchase a digital multi-meter for monitoring receiver battery packs, as they are useful for other things (checking none-chargeable batteries, testing fuses and light bulbs, measuring skin resistance to see how stressed you after your model crashes because you didn’t check the batteries – that sort of thing).

Maplin can provide one for a mere £12.99 that will do the job nicely. Alternatively a number of dedicated battery checkers are available in model shops and specialist outlets e.g. SM Services.

One other mode of battery, failure oft overlooked is ‘crash’ damage. Always check your batteries after a crash as mechanical failure of solder joints etc can lead to poor and/or intermittent contact that will come back and bite you next time out. Try to ‘wiggle’ connections and pull on wires while operating a servo to check for problems.

Another failure mode, although not strictly battery failure is ‘black wire corrosion’. If you examine an old battery pack which has lost its punch you may find the wire coming from the negative terminal is corroded, black in colour, brittle and impossible to solder. It is usually corroded for its whole length, from the negative terminal right up to the switch or plug. The cause of black wire corrosion is not clear, but is probably the escape of potassium hydroxide from the inside of the cell. However, the cause isn’t important - just examine your batteries occasionally to ensure they are not suffering from it. If you find black wire corrosion, the pack is useless and should be discarded. It is a waste of time trying to press it back into service by soldering on a new lead and plug.

One or two other modes of battery failure are sometimes cited. However if the battery is charged properly, not left on a slow charger indefinitely and not discharged to ‘flat’ very often, these other failure modes will be unlikely to trouble you.

NiCd/NiMH Storage

No special precautions are required generally in this country (UK). Disconnect from your equipment to decrease the chances of black wire corrosion. If you expect the temperatures to be consistently above 30°C with high humidity then you can put the batteries in the fridge, not the freezer. On removal from storage, slow charge for the first time before use, as they will normally be flat due to self-discharge. Do not fast charge as there is an outside chance that you could damage on of the cells of the pack due to ‘cell reversal’. If batteries are to be left in storage for more than 12 months, it is a good idea to charge them periodically, say once every 6 months. After long-term storage, it will take a few cycles of charge/discharge to reach maximum capacity.

NiCd Myths

There are a number of myths surrounding the use of NiCd (and to some extent NiMH batteries) including “Memory Effect” and the need to “Cycle” your batteries. The last is probably a ‘sub-myth’ of the first. Frankly, I do not believe either, nor can I find any solid scientific proof of either; lots of apocryphal stories but no hard evidence, and believe me I have tried!

“The Memory Effect”

The Memory Effect defined as a loss of capacity due to repeated discharges of less than 100% does not and has not ever existed in the types of NiCd batteries you are using in your model. Period.

True Memory Effect only ever happened in sintered plate NiCd cells and it only happens when you precisely discharge a cell to exactly the same level over and over again, and recharge it without any overcharge. True memory effect happens in satellite power systems, electronics test labs, and practically nowhere else.

Even if you were using sintered plate NiCd cells you do not discharge them by precisely the same amount each and every time you use them. You also never charge them to exactly the same point with out overcharging.  Therefore,

you cannot induce memory into your batteries.

Remember that if nothing else.

“What did I have to remember

about memory effect?”

On some electronic systems (e.g. mobile phones, Walkmans etc) which switch off at a precise point defined by a voltage measuring circuit, you can get an apparent loss of capacity. This is due to the cell voltage being ‘depressed’ or reduced by repeated overcharging. This reduction in cell voltage causes the voltage sensing circuit to declare “Flat Battery” before it should. In fact, there is plenty of charge left; the battery is just operating at a very slightly lower voltage. It is not ‘memory’. In addition, it does not occur with your radio system as your radio system does not switch off at any point defined by a precise voltage sensor (it would be fun if it did – NOT!).

In equipment with a voltage determined end point, the problem can be cured by fully discharging the battery and recharging, and this has lead to the second myth;- the need to cycle NiCd batteries.

“The Cycling Myth”

I have described above that there is a limit to the NiXX battery life defined by the number of charge/discharge cycles. I have also told you that battery memory is a myth, and apparent loss of capacity due to voltage depression does not happen with our model radio systems. Ergo: there is no need to cycle your batteries. In fact, you will reduce their life, albeit marginally, if you do.

There is some evidence that very slow charging or operating at high temperatures can lead to ‘large’ cadmium crystal growth. This in turn can lead to higher internal resistance and voltage depression without overcharging. Again, this can be cured by discharging fully. However, it is extremely unlikely to happen with model radio batteries; even our slow chargers are not slow enough to cause this effect.

So you do not need to cycle your batteries (just ‘re-cycle’ them when you eventually dispose of them after many years good service).

If you still don’t believe me and want to cycle them, just do so occasionally, but don’t bother with a special discharger. Just leave the system on for a few hours until the receiver or transmitter stops working, then recharge with a slow charge. I do this occasionally – not consciously, I just forget to switch the damn radio off once in a while!

I couldn't find a picture of battery cycling so I have used this picture of 'batty' cyclists instead!

Therefore, in summary then, to look after your NiXX batteries apply the following simple rules:

* DON'T deliberately discharge the batteries to avoid memory

* DO let the cells discharge on occasion through normal use.

* DON'T leave the cells on trickle charge for long times

* DO protect the cells from high temperature both in charging and in storage.

* DON'T overcharge the cells.  Use a good charging technique.

* DO get a battery monitor or multi-meter and check the self-discharge rate if you think the batteries are getting long in the tooth.

Well that's it for now on NiCds and lead acid. I will post some notes on Lithium when I have time and I'm confident that I know what I'm talking about. Happy Landings.

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