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Old 03-20-2008, 04:41 AM   #1
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Default Bringing batteries back to life

Hi all,

I have a box full of old GP 3700s... when I put them into my charger, they show around 0.6V.

I have tried several things, but I can't seem to bring them back to life...

I have tried cycling at 0.5A charge/0.5A discharge... this works, but as soon as I try to charge at around 3.7A/3.7A discharge, the cell charges at ~1000mAh and discharges only 100mAh.

One of the cells I tried 3.7/3.7 on yesterday vented on me.

Should I just go through more 0.5/0.5A cycles, and slowly up the current as I go along?

Or do you have any other better methods of bringing batteries back to life? I also thought about doing a little bit of flex charging on them, but that is only recommended for NiCd as far as I gather?

Thanks in advance.
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Old 03-20-2008, 07:36 AM   #2
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ok, this is my method i use for old laptop cells and such like. i managed to get some 15 year old 1800 ni-mh's back to about 1300mah this way.

1. leave them at 300mah for a few days on a power supply at 1.5v/cell.

2. use a pulse width modulation charger, or the one you can safely charge alkalines with to cycle the individual cells a couple of times.

3. drop the cells from 6 feet onto a concrete floor (positive cap up! thats the weak spot) to knock the crystals off the inside, and charge on the PWM cahrger again. repeat this process a few times. i was shooting mine with a BB gun instead of dropping them too.

4. after a few cycles of this method i simply charged them up using a normal ni-mh household charger, made into a pack and used it. (only for a portable amplifier though. the cells were in such bad shape they only gave about 1C)

ok, it seems destructive but it seems to work...
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Old 03-21-2008, 04:53 AM   #3
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Thank you,

any other opinions?
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Old 03-21-2008, 05:58 AM   #4
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bringing batteries back to life....


Try a "ZAPPER" once or twice!

Last edited by il-gufo; 03-21-2008 at 11:13 AM.
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Old 03-21-2008, 06:39 AM   #5
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tray them untill all the cells are at "0" volts. Then deadshort them by soldering a wire from the neg. to pos. ends of a complete pack. Let them sit for a while and then charge the pack at 5.0 amps. cycle them a few times but be sure to tray them down to zero volts before shorting them.
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Old 03-22-2008, 10:55 AM   #6
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No no. If the cells are still good, put a little charge in them (1000mah) and let them sit for a few days. Then discharge them and charge them back up.
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Old 03-26-2008, 10:16 AM   #7
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I tried charging them using flex charge on my Cell Master...

I started off low (0.5A) with a lot of flex (7), and kept upping the amps after 3 cycles... when I reached around 3.7A, I started lowering the flex all the way to 0 after a few more cycles...

The batts now discharge at around 5A np, not great, but OK I guess...
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