How do I resurrect old NiMH batteries?

[filibuster]

I found eight Amondotech Titanium 850 AAA NiMh batteries in my closet the other day. They are about three or four years old still in their original four pack shrink wrap.

I split one set apart and stuck them in my Maha MH-C9000 charger and did a break-in charge but after it finished the cycle the batteries only registered 350-380 mah. I next performed a 3 cycle charge discharge test but even after that the four batteries ended between 450-500 mah. A little improvement but still a long way from rated capacity.

Will continued cycling restore the batteries capacity or is long storage without use the death knell of a NiMH battery?

Can you jolt a cell back to good form by using a high charge rate or a high discharge rate or is it better to do many low charge and discharge to try and persuade the capacity back into the cells?

 

[Mr Happy]

They might be beyond rescue.

You can keep doing charge/discharge cycles while the capacity continues to improve after each cycle. You might try another break-in cycle too.

Next time, try measuring the voltage on the cells before you charge them. If the voltage is above 1.0 V you have a chance to get the cells back, but if the voltage is down near 0 V then they have probably suffered degradation in storage.

 

[rizky_p]

Most likely they are dead. You can try cycling it several times just in case one of the can be ressurected

 

[Black Rose]

I had a similar issue with some other cells.

I started doing 0.5C charge and 0.25C discharge cycles, but they didn't improve much. I ended up doing several 0.5C charge/discharge cycles, and they did come back a bit more.

I may give them a 1C charge/0.5C discharge and see what that does.

 

[TorchBoy]

There was a similar thread here a week ago. It doesn't sound promising for cells left that long.

 

[Trashman]

The lacrosse chargers (BC-700/BC-900) have a refresh function that does 20 discharge/charge cycles. Maybe, if you keep doing the 3 cycle charge/discharge test, you'll see some more improvement.

 

[Fallingwater]

Keep in mind that four years in storage are likely to drop the voltage far under the safe limit. Even if they have something vaguely approaching their original capacity, their self-discharge must be stupidly high. Expect to find them stone dead after a day or three from the last charge.