Strange rapid self discharge

[supergrade]

My current battery stock is mostly Energizer AA 2500s (yeah yeah, don't say it - Sanyos on order) many of a few year's age. They have generally seen use in wireless remote controllers for game systems or wireless mice.

My charger is the Maha C9000

I noticed something strange with a couple of pairs of batteries running dead (not able to run the device) very rapidly, under very minor use. On putting the pairs on for discharge, one still had 70-80% of charge and one was dead.

I isolated a pair and did a whole bunch of discharge/refresh/breakin. I can charge/discharge them to 1900+ (500ma discharge) right after charge. But after sitting for 2 to 3 days, they will only discharge to ~1000. This is very different to all the others.

Any ideas? Is there any shock treatment that will alter the self-discharge rate? Are they writeoffs, or is there a regimen (number of breakins, etc - I have a MAHA C9000) to make them useful in remotes again? I used to think that age just affected capacity or chargeability - these will hold 2000, just not for long.

Any insight appreciated.

 

[Turak]

You've been bit by the Energizer 2500 'self-discharge' problem.

Seriously, all batteries self-discharge to an extent.

The problem is that as the industry strived to pack more mAh into a battery, so they could print a larger number on it (since many uninformed users just think the bigger the number, the better the battery).....they were creating another problem.

In order to get more into the same space..something had to give. It ended up being the separator material got thinner and thinner, with more material jammed into the same space, everything got tighter and tighter. THe material inside actually expands as the battery gets warmer. This is why the first few uses seem OK and then many of them develop the horrible self-discharge problem. THe material inside the cell has expanded and everything is pressed tightly against everything else. With the thinner or damaged separators, they self-discharge faster.

Suddenly...extreme self-discharge became a BIG problem.

The Energizer 2500's are notorious for being the worst regarding this problem. Search the forum and you will see.

There is NO WAY to 'really' fix a Ni-Mh cell when it develops high self-discharge. Chuck the cells and replace them with some LSD type cells, 'Eneloops or Duraloops' are some of the best. You won't be sorry.

So... Now you see that you REALLY need to test your batteries at least 2 ways: One test for overall capacity and one test for high self-discharge. I use the following guidelines, enhanced with a little information from the Sanyo, Duracell, Maha, and LaCrosse websites.

Regarding capacity... When a battery can no longer reach 80% capacity, even after 2 or 3 B/I cycles on the MH-C9000 or 85% after 2 Discharge/Refresh cycles on a BC-900, I dispose of them and replace them with LSD type cells.

Regarding the 'self-discharge'.... When using regular Ni-Mh cells I charge them up fully and then set them aside for 7 days. I then run a discharge on them with the MH-C9000 and when they can no longer retain 80% of their 'tested' max capacity, I dispose of them and replace them with LSD type cells. Sanyo and Duracell charts show they should retain about 85-90% of their capacity at 20'C (about 68'F) after about 7-10 days.

 

[yellow]

out of every 4-pack of any cells (1900-2800 mAh) I bought the last years, at least one shows similar ...

Not so the LSDs I have now (Eneloops and Uniross Hybrio "precharged").

Also all of them achieve the discharge readings You posted and have that low discharge bonus
(after one week of resting 2 out of every 4-pack of "normal" cells were way below the LSDs)

With Your readings it makes no sense to use those "high capacity" cells, and if You are - like me - one of these guys, who not always charge the cells prior to the use,

You are also a candidate:
get LSDs