NiMH 0 volts, safe to recharge?

[ImGeo]

I have a bike light which uses 2 AAA Royovac Hybrid batteries. I've been using rechargeables, and never recharged it for a long while. Today, the light didn't work, and a check on the battery returned 1.16v and -0.04v - is it safe to just recharge the battery and continue using? I'll probably be testing the capacity again after I charge it with my LaCrosse BC 700

 

[csshih]

it should be safe to recharge it..
nimh isn't dangerous when compared to li-ion.

 

[Bright+]

Polarity reversal is cumulatively damaging. If it's -0.04v, that cell is weak and it most likely be the first to become empty again and becoming further damaged. It will be a vicious cycle.

Don't worry about memory effect and don't deep discharge multi-cell package to the point any one cell may drain to 0v. It's better to charge with 25% charge remaining than to let anything go into reversal.

Memory effect is not a big issue on NiMH and apparently only happens when the depth of partial discharge is always the same point, for example, fully charge, run five minutes and repeat.

 

[paulr]

The cell that was reverse charged is probably shot. Don't expect it to hold a charge. I'd use the good cell in a 1-cell light and get a new pair of aaa nimh for your bike light, so they will be matched.

 

[zipplet]

The cell that was reverse charged is probably shot. Don't expect it to hold a charge. I'd use the good cell in a 1-cell light and get a new pair of aaa nimh for your bike light, so they will be matched.

This is the best advice even though it costs you a very small amount of $$$. I failed to heed this advice with some GP 2700's in my L2D-RB100 a while ago and the problem got worse, to the point that the cells in the light would gas a lot and one cell hardly held any charge at all (1000mAh).

 

[DScottHewitt]

The cell that was reverse charged is probably shot. Don't expect it to hold a charge. I'd use the good cell in a 1-cell light and get a new pair of aaa nimh for your bike light, so they will be matched.

I am far from an expert, but I would tend to agree that the negative charge battery is probably not salvageable. And I would agree use the other battery by itself in something that takes a single cell and get a new set for the bike light.

 

[Mad-Bassist]

Eneloop abuse

You may have trouble if your charger can't tell you inserted it. To somewhat repeat the previous poster, the only danger would be using the damaged cell with others because of the difference in capacity, which would accelerate the damage once it's run down compared to the other cell(s). Best to use it for a one-cell application if it still works.

I once had a set of four AA Eneloops that died in my Fuji Finepix camera after sitting unused over a year and a half. Little did I know that camera drains a few microamps or so to keep the memory intact. (I had to reset everything.)

One cell showed zero volts, one had 0.3 or so, and the other two were around 0.7. I ran a refresh-analyze cycle on them with my Maha, and the capacities are now 1657, 1971, 1994, & 2004. The first two now work cordless mouse duty (A Rosewill that uses one cell at a time, and takes over a month to run down.) Not bad for batteries I bought in 2007. They've been recharged only about a dozen times, and for the most-abused one to still have 1657mah after probably being reversed says good things about Eneloops.

 

[Helmut.G]

Re: Eneloop abuse

well, if your charger can't handle it, damaged cells could seriously overheat. apart from that the biggest safety issue is being left in the dark while riding your bike at high speeds. I recommend you get new cells.