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What is needed to conduct a life test on a rechargeable battery for a 2way radio? The chemistry is NiMH. I have battery analyzer to tell me capacity of new batteries, but I need to figure out how to determine the longevity of the cells.

We are suspecting the cells for the batteries we purchasing are not lasting as long. How do I prove it?

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There is no certain way to do this but there are indicative ways.

Very important is brand. Are thse a reputable brand and are they genuine. Most good quality NimH cells are made by GP, BYD or BPI - regardless of the label. GP is HK based, China mainland made and BYD and BPI are Chinese. GP are often sold uner their owen label (GP, Goldpeak, ReCyko) and are heavily counterfeited in Asia. Beware.

FIRST weigh the cells. This is a measure of mAh capacity and nmot of longevity BUT if the longevity is poor the mAh are probably also poor.
If these are AA NiMh you are probably using claimed 2500 mAh or more. These should weigh not much less than 30 grams (1 ounce) and prefereably somewhat more. 35 grams would be unusually high. 25 grams is too low.

If these are not AA then scale by about Claimed_mAh/2500 x 30 grams ~= mAh/80 grams. Weighing a few samples of different brands of the same size will help.


THEN:

You need to have a proper idea of what is claimed for the cells and whether you are using them in a manner that is consistent with the makers guarantee. Many cells are rated under standard IEC test regimes which poorly match actual use.

Also, how you charge and discharge cells can substantially affect lifetime. Cutoff on discharge should be no lower than 1.0V on heavy load and 1.1V on light load. Charging meeds to terminate correctly by whatever means used. Charge time should not be less than 1 hour rate and stopping on -delta Voltage and on +delta temperature and on absolute temperature is desirable.

Proper cell cycling to formal IEC cycle is annoyingly slow with rest period after each charge and discharge. Also IEC rates may be 10% of C so a single charge discharge cycle may take a whole day.

Your radio will have a discharge rate - probably many hours of use on receive. Less on transmit.

You can perform indicative testing using fast charge/discharge methods and use some known good cells to compare. Charge at say 1C rate (mA = mAh) and terminate using standard means OR charge for say exactly one hour (less preferred). Then discharge at 1C rate to 1.0V terminal coltage. Time this cycle (preferable charge and discharge times), log and repeat. This will give you 8 to 10 cycles per day. At one month you should have a very good idea of how well the cells are holding up.

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