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NiMH batteries info and charging Do's and Don'ts


Fly In My Soup

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NiMH Rechargeable Batteries

This guide, has been compiled from a few different guides and added to by me for the forum

 

As some members, and also new members to come who are just entering the hobby are still making use of NiMH batteries, wether for the RC itself, or your transmitter, this brief guide may help answer some questions

 

Links to other related guides are highlighted in orange!

 

NiMH batteries

 

If you’ve ever bought an RTR RC chances are you've  used a NiMH battery at some point, maybe you also use NiMH AA and AAA devices in your life, you’ve probably at least considered investing in some rechargeable batteries. NiMH cells have soared in popularity as devices have become increasingly wire-free, and thus battery-dependent.

 

Wether your using them for RC or for any other device, Rechargeable NiMH are a great idea all around: they save you the hassle and money of repeatedly buying throw-aways, and also keep those single-use cells out of the landfills. 

 

55-16076-nimh_teaser.jpg

 

How NiMH batteries work

A NiMH battery consists of two metal strips, which act as the positive and negative electrodes, and an insulating foil separator that goes between them. This delicious energy sandwich is coiled up and placed into a battery canister along with an electrolyte liquid. The positive electrode is typically made of nickle, the negative of a metal hydride, hence the name “NiMH” or “Nickle-Metal Hydride.”
 

55-16079-batt_close.jpeg


ProtekRC3000NiMh.jpg
Put that dead battery into a charger, though, and the electrical current reverses the discharge process. Electrons are pulled out of the positive electrode, causing it to oxidize and release hydrogen. At the same time, electrons are put back into the negative electrode, and it absorbs hydrogen. In the case of an extreme overcharge, any excess hydrogen gets vented out the top of the battery—look closely at the cap on your rechargeables and you’ll see the vents.
 

How to keep your batteries healthy-the facts and fiction

In talking about rechargeable batteries, there are two terms that get debated endlessly: “memory effect” and “voltage depression.” With even a quick search, you’ll find all sorts of conflicting information on both phenomena, but few scientific tests to confirm them. Complicating the issue further, these two problems make for excellent scapegoats, and are often blamed when batteries suffer any kind of failure. So what are these issues, and do you need to worry about them?
 

55-16078-charge_station.jpeg
Nimh_Battery_4600mah_SC_Size_Nimh_Rechar
Some people don't know that NiMH batteries 

do not have a “memory effect” —it’s a issue only found in Nickle Cadmium batteries , and even then it’s difficult to replicate.

“Voltage depression,” on the other hand, can happen to NiMH batteries, though it’s questionable how noticeable it is . When a battery is repeatedly overcharged, small crystals form on the electrodes, inhibiting their ability to complete that important chemical reaction. As a result, the battery’s voltage drops. And even though that drop shouldn’t affect the battery’s capacity, it can cause a device to think the battery is losing charge faster than it truly is.

For both conditions, the standard advice is to discharge your batteries completely, then recharge them. And while that is a sound treatment for both “memory effect” (in nickle cadmium batteries) and “voltage depression,” it’s also an easy way to damage your NiMHs—over discharging can cause “ pole reversal ,” which permanently damages a battery. Some electronics are made to prevent this, shutting down before reversal can happen, but simpler devices like flashlights often don’t.

55-16077-eneloop.jpg

 

So how should you actually handle your NiMH batteries?

Past all the confusion, there is some very solid, consistent advice about getting the most out of your batteries.

1. Be prepared to replace them, eventually. NiMH batteries don’t last forever, and though time and use they will stop working. Thank them for saving you money, recycle them, and move on.

2. Buy the best charger you can afford. You don’t have to spend a fortune on the best charger available, but make sure you get a “smart” charger, one that electronically monitors the recharge process and prevents overcharging. Not only is it better for the batteries, it will use less power than cheap chargers, which often rely on a simple timer mechanism. 

 

3. Don't overcharge, don't under (trickle) charge Nimh batteries should never be overcharged, the maximum capacity for any NiMH battery is 120% (which is what your NiMH charger SHOULD charge your NiMH batteries to before auto shut off, @Rudd looking at you)

And in the same breath, NiMH batteries with a capacity above 900mah should never be charged below 0.5a ( referred to as trickle charging ) as this fails to enable the battery cells to absorb voltage in the same way as if a higher current of charge as applied, which can itself lead 'ghost' charging (when a battery appears full but is actually storing very little energy ) and capacity depletion on a more accelerated scale.

 


4. Remove the batteries when the recharge is complete. Unnecessary time on the charger means more “trickle” power is used to keep them charged—so more wear and tear and more wasted power, also heat starts to build in the cells, further damaging the electrolyte compound contained within.

5. Don’t regularly discharge your batteries completely in an attempt to make them last longer. Despite all the advice to the contrary, complete discharge can actually shorten their lifespan.

6. Store your NiMH batteries at room temperature in a dry location. Excessive heat can definitely damage your batteries and cause them to lose charge faster. 

7. Consider using low self-discharge battery model for your transmitter. Eneloop is the best known brand of these batteries, which unlike most NiMH cells don’t lose power as quickly when sitting on a shelf. If your rechargeables are ready to go, you’re less likely to fall back on the throwaways.

 

8. Cell packing?

 

Some may have heard of battery cell 'packing', a useful way to enable you to get the most out of your NiMH batteries everytime you charge them for use....basically put in an example here;

 

Slow charge your NiMH battery the night before using on 1a current, charge until charger declares the battery full, then leave it to rest overnight....when you wake you should take the battery and charge it again, this time on 4a, for a brief period (around 20 minutes or until the battery gets hot)

 

This, in essence, is 'packing' the cells with a truly full charge

 

ov2588g__54446.1462544675.520.520.jpg?c=

 

Now I'm off to recharge myself....with a coffee..

 

 

HOW DO I STORE MY Nimh BATTERIES??

 

well the answer to that question depends on a few factors, type of nimh batteries, storage timeframe etc etc.... So I'll do my best to break down the info so its easier to read

 

First point to remember, not all NiMH batts are created equal!

 

• Storage temperature and humidity

Any type of NiMH cells need to be stored between 10-25°, if the temp is too high then self discharge will be accelerated, so no storing them in the shed or near a heat source!! And humidity should be roughly 40% , a great way to achieve this is too store multiple NiMH batts in a large Tupperware with a tobacco humidity disc popped in with them.....that's the fundamentals covered.

 

 

• Storing standard NiMH cell packs (short term - under 8 weeks)

If you plan to store your standard NiMH cells simply until the next weekends bash, then it couldn't be simpler, just ensure your batteries are roughly 60-% charged at time of storage and simply charge as usual the next time you use them.

 

• Storing standard NiMH cells ( long term - 8 weeks to 10 years+)

if you're planning on storing NiMH cells for a long time, simply ensuring their at 60% charge level is not the end of the job...... Why?... due to self discharge ...... So you're going to check your batts every 8 weeks to ensure the voltage doesn't drop below 20%, you'll probably see a small drop in voltage across the pack if you stick to checking every 8 weeks.

 

• Why shouldn't I let the batteries go below 20%?

Nimh batteries should not be left to drop a significant amount in voltage, known as under-voltage, as over time it causes a decrease in the cells capacity

 

To better understand this technically, we can look at the reason why standard NiMH batteries self discharge when not in use

 

The reasons for this self-discharge of Nickel-Metal Hydride batteries are as follows:

 

  • The core of the NiMH cell contains a hydrogen atmosphere which is a at low pressure, this gradually reduces the active materials at the +ve electrode, resulting in a reduction of cell capacity. Accompanied by this, the -ve electrode which is thermo-dynamically unstable in its charged state gradually emits hydrogen gas, also reducing the cell capacity of the NiMH battery.
  • The active materials contained at the +ve electrode whilst in its charged state self-decompose, causing the cell capacity to decrease. 
  • Impurities within the NiMH cell, especially the nitric ions, are reduced at the -ve electrode and are attracted to the +ve electrode where they are oxidized. This also contributes to the resultant reduction of cell capacity. 

 

• Cycling

No need to worry...not the kind that involves lycra ....cycling is the process of slow charging at 0.5-1A until full, then slow discharging at 1c back down to 60% , then repeat three times.

 

it will be necessary to cycle the battery in this way after prolonged storage to, amongst other things, restore capacity.

 

*non standard NiMH cell batteries ( twicell, Low.Self.Discharge)

 

As technology improves, more companies are offering LSD NiMH batteries (Panasonic,varta etc)

Which does exactly what it says on the tin! Nominal self discharge enables the user to store the cell at virtually any voltage for extended periods of time, although they may take 7 cycles to recover capacity if stored at a greatly reduced voltage

 

 

 

 

The following information on how to format a new NiMH battery only relates to formatting a NEW NiMH battery

 

 

Why is my new NiMH battery giving depleted runtime and won't take charge???

 

This happens to most nickel based rechargeable batteries, and is caused by a settling of electrolytes within the internal composition.

 

This can be rectified by formatting a battery.

 

 

 

Below is advise in formatting a new battery from a well known manufacturer

 

 

We advise to trickle charge a nickel-based battery for 16–24 hours when new and after a long storage. This allows the cells to adjust to each other and to bring them to an equal charge level. A slow charge also helps to redistribute the electrolyte to eliminate dry spots on the separator that might have developed by gravitation.

Nickel-based batteries are not always fully formatted when leaving the factory. Applying several charge/discharge cycles through normal use or with a battery analyzer completes the formatting process. The number of cycles required to attain full capacity differs between cell manufacturers. Quality cells perform to specification after 5–7 cycles, while lower-cost alternatives may need 50 or more cycles to reach acceptable capacity levels.

Lack of formatting causes a problem when the user expects a new battery to work at full capacity out of the box. Organizations using batteries for mission-critical applications should verify the performance through a discharge/charge cycle as part of quality control. The “prime” program of automated battery analyzers (Cadex) applies as many cycles as needed to attain full capacity.

Cycling also restores lost capacity when a nickel-based battery has been stored for a few months. Storage time, state-of-charge and temperature under which the battery is stored govern the ease of recovery. The longer the storage and the warmer the temperature, the more cycles will be required to regain full capacity. Battery analyzers help in the priming functions and assure that the desired capacity has been achieved.

 

 

Edited by Fly In My Soup
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Nice guide mate. You forgot or i missed it. Nihm are just as volatile as lipo. I heard a kid on here his sister threw his nihm at him. It bounced off the wall and exploded BANG. Worst story i seen on nihm. The reason i deceided to use lipo too. Since both can be dangerous stuff it lol. 

 

Idk if i over charge mine but they do get hot at times. But i think i usually under charge being impatient. I need to replace it mayb. 

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  • 2 months later...

You say that NiMHs should never be charged below 0.5a but I read on rctech that you should trickle charge at 0.1 for up to 24 hours on the first 3 Charge’s to correctly balance and ‘form’ them. 

 

The charger I have for my 1300mah is 500ma and takes approx 2-2.5 hours to charge but the cells closer to the plug get warmer than the other end which are cold. Does this mean the cells aren’t balanced and should have been trickle charged? 

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On 11/02/2018 at 23:38, Nickarla said:

You say that NiMHs should never be charged below 0.5a but I read on rctech that you should trickle charge at 0.1 for up to 24 hours on the first 3 Charge’s to correctly balance and ‘form’ them. 

 

Well if you will visit inferior forums like that one.....expect inferior advice:lol:

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On 20/11/2017 at 16:37, Fly In My Soup said:

And in the same breath, NiMH batteries with a capacity above 900mah should never be charged below 0.5a ( referred to as trickle charging ) as this fails to enable the battery cells to absorb voltage in the same way as if a higher current of charge as applied, which can itself lead 'ghost' charging (when a battery appears full but is actually storing very little energy ) and capacity depletion on a more accelerated scale.

 

On 11/02/2018 at 23:38, Nickarla said:

but I read on rctech that you should trickle charge at 0.1 for up to 24 hours

 

:rolleyes:

 

Above is the reason not to charge Nimh at that rate

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In the end, I only have the one charger which is 0.5a so that is what I charge with. I don’t notice any run time problems despite some cells feeling more warm than others...doesn’t seem to affect performance though.

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5 hours ago, Isle of Wight Basher said:

it's probably better to state the charging rate as a C value.

 

That's not correct

 

Coulomb's are different to Amperes, Ah and Mah

 

They're 2 different units of measurement, although they are both used to measure current

 

 

Amperes are used to measure flow of current ( resistance), whereas Coulombs measure the amount of charge.

 

Unlike coulomb, which measures the amount of charge, ampere measures how fast the amount of charge is moving. This is the key difference between Ampere and Coulomb.

 

Hence why your batteries have three figures on the label , measured in units from the Si table.....voltage, Mah, and C.......and also why you'll find  a NiMH charger measures current going into a battery in Ah ....not C.

 

Manufacturers adhere to these Si based units, often by law

 

Also , it can be confusing, as the battery industry alone chooses to use Mah....not ah or A......this can get even more confusing as 1 ampere is roughly linear to 1 Coulomb, whereas 1 Ah =3600c......or as you see on a battery .....Mah,

 

 

An ampere hour or amp hour (symbol Ah; also denoted A·h or A h) is a unit of electric charge, having dimensions of electric current multiplied by time, equal to the charge transferred by a steady current of one ampere flowing for one hour, or 3600 coulombs.[1] The commonly seen milliampere hour (mAh or mA·h) is one-thousandth of an ampere hour (3.6 coulombs).

 

 

 

What is Ampere?

The measuring unit of current, Ampere, is named after a French mathematician and physicist André-Marie Ampère who is considered as the father of electrodynamics. Amperes are also called as amps, in short.

 

What is Coulomb?

The SI unit Coulomb, which is used to measure electric charges, is named after the physicist Charles-Augustin de Coulomb who introduced Coulomb’s law. Coulomb’s law states that when two charges q1 and q2are placed r distance apart, a force acts on each charge according to:

F = (keq1q2)/r

 

 

So I think it's probably best to follow the rest of the industry and stick to Ah for unit of input charge, and C for a general discharge rating

Edited by Fly In My Soup
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For anyone wishing to work out they're input charge rate in C, here's two examples of the equation;

 

 equation below shows the relationship between charge, current and time:

charge (coulomb, C) = current (ampere, A) × time (second, s)

 

 

Or this equation

 

 

1 Coloumb is 1 Ampere of current flowing for 1 second.

1 Ampere is 1 Coloumb of charge flowing per second.


Q= I × t

I = Q / t

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37 minutes ago, Isle of Wight Basher said:

I wasn't talking  about Coulomb's, but C as in Capacity. Excellent cut and pasting skills though.

 

I truly can't be arsed with posting here anymore,  your knowledge is limited, but not in your mind.

 

Peace, Out.

 

Oh here we go, another one crying......

 

No one forced you to post incorrect information on my thread, you did that by yourself...... with conviction

 

FYI, most of that stuff IS copied from other sites, mainly because I actually double check facts that I assume are correct, then I copy and paste the info to show to people like you.

 

P.s my assumptions come from 3 years of college studying electrics and a further 10 in the auto electrical industry.

 

 

Oh and just so you know....

 

Ah is the unit for measuring Capacity in a battery.....the symbol C stands for coulombs

 

I may get it wrong sometimes....but at least I've got the manhood down there to admit it......

 

Peace out to you to 

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  • 2 weeks later...
2 hours ago, ChrisT said:

@Fly In My Soup

 

Excellent write up, I pretty much adhere to those guidelines.

 

One thing I'm uncertain of. Whats the best way to store Nimh when not in use for weeks or months even?

 

Discharged?

Half charged?

Full charge?

 

I've added to the guide for you dude, see the end

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Do NiMh suffer from 'black wire corrosion' as NiCd was said (by some) to do.

 

Spot the one who went straight from NiCd to LiPo (life got inbetween).

Edited by soup
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36 minutes ago, soup said:

Do NiMh suffer from 'black wire corrosion' as NiCd was said (by some) to do.

 

Spot the one who went straight from NiCd to LiPo (life got inbetween).

 

Showing your age their dude!

 

In short , technically yes.....and no

 

There's two causes of black wire corrosion/rot, so called because it effects only the - ( black, negative) wire in DC systems using a battery for a power source ( excluding lipo, life)

 

The main cause in an rc based nicd/nimh cell packs stems from overcharging.

 

Back when chargers used timers, battery packs where set up on trickle charge for say 10 hours, usually overnight, but would be fully charged by 8 hours, leading to 2 hours of overcharge....and as you'll note from info further up this thread, this causes the battery to vent gas, continuously doing this time and time again causes 'creap leakage' of ,amongst other things, caustic material called KOH within the cell packs wrap, once this hits the terminals and wires it will induce the famed 'black wire' rot

 

The second cause, and most prolific, can affect any DC based circuit, whereby the power source is put under constant load, resulting in high resistance in your negative (black ) wire, over time this creates heat....and with heat you get condensation......when these factors combine with chemicals in the PVC and wire lube agent, a chemical reaction occurs, turning the copper black with chemical oxidization 

 

So why yes and no??

 

Few reasons

 

Most rc cell pack makers now use high grade silicone to insulate their leads/wires, instead of PVC

 

Also, thanks to advances in technology, a lot of copper wiring is now coated in a 'varnish' to prevent wire oxidization.

 

Overcharging is not really an issue these days, thanks to chargers using an auto cut off when full, so no overcharging occurs

 

 

Edited by Fly In My Soup
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I'm slightly confused about the "formatting" of a new battery. 

 

The first post suggests charging the battery for 16-24 hours on a trickle charge.

However, it is noted that charging at rates under 0.5amp is not recommended.

 

If we have a 5000mah battery and charge it at 0.5 amp, its going to be fully charged in say, 11 hours or so.

At that point I understand that intelligent chargers will now "trickle charge" - so presumably at a rate lower than 0.5 amp ? which we don't want ?

Or does it just stop charging ? so the 16-24 hour charge time isn't achieved ?

 

 

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2 hours ago, Mark_C said:

I'm slightly confused about the "formatting" of a new battery. 

 

The first post suggests charging the battery for 16-24 hours on a trickle charge.

However, it is noted that charging at rates under 0.5amp is not recommended.

 

If we have a 5000mah battery and charge it at 0.5 amp, its going to be fully charged in say, 11 hours or so.

At that point I understand that intelligent chargers will now "trickle charge" - so presumably at a rate lower than 0.5 amp ? which we don't want ?

Or does it just stop charging ? so the 16-24 hour charge time isn't achieved ?

 

 

 

 

Apologies if its confused you dude!

 

Formatting...In lamens terms....is basically saying that a new battery needs a brief period of charges before the battery cells can provide maximum performance (including taking, holding and delivering a charge)

 

So what your experiencing (low performance) is perfectly Normal for a new NiMH battery.

 

To format a NEW NiMH battery;

 

- Trickle charge it on 0.5A until full

- discharge it on trickle discharge (0.5a)

 

Repeat this process around 5-10 times, then your battery will be 80-90% formatted.

 

Then you can charge your battery as normal

 

Battery performance will increase after formatting and will continue to increase with normal usage ( charging and using in rc )

 

P.s the info in the first post is about charging a USED NiMH, one that's already been formatted then used in an rc a dozen times, should not be trickle charged (see first post) 

 

Does that help???????

 

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Ok, so a constant cycle of charge and discharge for 16-24 (or whatever). Thanks.

 

The charger I have doesn't have a discharge facility (its just a cheap one). I'm dubious of the bmax i6 given the number of dodgy clones out there. 

Is an Overlander RC6-VSR decent enough ? any alternatives ?

 

Am I correct in saying for nimh you don't need a dual charger, you can just create a lead with two battery connectors and charge 2 at the same time, effectively the charger would see a (say) 10,000 mah, 12 cell battery rather than a 500mah, 6 cell battery ? so a 0.5 amp charge would take 20+ hours ?

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No need to get a new charger, although I will say that the old NiMH chargers ( delta  peak) are better for charging NiMH IMO ....

 

Also, you can use anything that's low draw to discharge during formatting

 

I've seen some folks use a lightbulb/torch etc etc

 

I wouldnt attempt to charge NiMH batteries off one charger dude, mainly due to the charger not being capable of charging NiMH in parallel or series very well...they struggle to cope with charging NiMH batteries with varying levels of discharge / capacity...which usually leads to over/undercharging in some of the batteries cells

 

There are some chargers out there that can cope with charging multiple NiMH and Nicad batts together, but they ain't cheap / discontinued..

 

Most companies have focused their attention on lipo batteries for these reasons.....ability to charge multiple batteries, also lipo batteries don't need formatting as they are ready from 'birth'

 

 

 

 

Edited by Fly In My Soup
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Really useful article. What's the advice for a battery that was never formatted (because I had no idea that was necessary), been used a handful of times and worked just fine, and now charges but once installed in the car behaves like an out-of-charge battery?

 

I have just tried charging at 1MaH and, unlike previous occasions, it was warm just after the charger said it was charged. Volt is showing at 8.3v but I've yet to try it in the car.

 

Thanks

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49 minutes ago, Fly In My Soup said:

No need to get a new charger, although I will say that the old NiMH chargers ( delta  peak) are better for charging NiMH IMO ....

 

Also, you can use anything that's low draw to discharge during formatting

 

I've seen some folks use a lightbulb/torch etc etc

 

I wouldnt attempt to charge NiMH batteries off one charger dude, mainly due to the charger not being capable of charging NiMH in parallel or series very well...they struggle to cope with charging NiMH batteries with varying levels of discharge / capacity...which usually leads to over/undercharging in some of the batteries cells

 

There are some chargers out there that can cope with charging multiple NiMH and Nicad batts together, but they ain't cheap / discontinued..

 

Most companies have focused their attention on lipo batteries for these reasons.....ability to charge multiple batteries, also lipo batteries don't need formatting as they are ready from 'birth'

 

 

Thanks, sticking with nimh for now because they are easier to handle/store and may only get used infrequently. Having a couple of chargers might be useful to me anyway, as I'll likely need two or more cars going at the same time, hence asking about dual charging.

 

It was simpler back in my day, twist the clock timer, wait impatiently, run car for 10 mins, rinse and repeat ! :) 

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24 minutes ago, themissingelf said:

Really useful article. What's the advice for a battery that was never formatted (because I had no idea that was necessary), been used a handful of times and worked just fine, and now charges but once installed in the car behaves like an out-of-charge battery?

 

I have just tried charging at 1MaH and, unlike previous occasions, it was warm just after the charger said it was charged. Volt is showing at 8.3v but I've yet to try it in the car.

 

Thanks

 

Just tried it in the car... Still behaves like a battery with no charge...

 

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6 hours ago, themissingelf said:

 

Just tried it in the car... Still behaves like a battery with no charge...

 

 

What your experiencing is commonly called 'ghost charging'

 

The battery appears to take charge (usually charging quite quickly) and shows as charged on the charger, but in reality the cells are not storing energy effectively anymore and as such...have decreased performance due to capacity depletion.

 

This is usually a symptom of overcharging, or just as importantly over-discharging, your battery ( see first post )

 

A NiMH battery that hasn't been formatted will have a reduced lifespan, but there may still be hope.

 

Cycling is your friend here!! It can help you partially recover the battery...see first post for cycling info dude

 

 

Edited by Fly In My Soup
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