Is it possible to rejuvinate a nickle metal hydride battery

[woody]

Can they be rejuvinated? Don't tell me about zapping them because that
doesn't work. Nor will freezing do anything for them. They charge up to
full voltage but have almost no current capacity. In a way this is like a
dead lead acid battery they to will ofton act like they have taken a charge but have no current capacity. Again the tricks used on nicad batterys don't help them.

[Conrad Hoffman]

IMO, for single cells, if deeply discharging them and recharging a few cycles doesn't help, they're toast.

[Elvee]

Originally Posted by woody

Can they be rejuvinated? Don't tell me about zapping them because that
doesn't work. Nor will freezing do anything for them. They charge up to
full voltage but have almost no current capacity. In a way this is like a
dead lead acid battery they to will ofton act like they have taken a charge but have no current capacity. Again the tricks used on nicad batterys don't help them.

Since they are not shorted, they have gone high-resistance. It is often caused by a loss of electrolyte, in which case nothing can be done (electrically at least).
But sometimes, they develop a sort of internal layering phenomenon, without any loss of electrolyte.
In these cases, I have found that "desulfators" for lead batteries can improve the situation, and in some cases revive them.
I am talking about the the ones that discharge an inductor into the elements.
The pulse energy has to be commensurate with the size of the elements, otherwise that will kill them for good.

[woody]

Thanks I may try that but I sure some one made a dirt cheap desulfator.
And here I am talking about the $10 price range.

[Elvee]

Originally Posted by woody

Thanks I may try that but I sure some one made a dirt cheap desulfator.
And here I am talking about the $10 price range.

I am talking about this kind of circuit:
Low Power Desulfator Info
They can be built for less than 10$.
I have made one with a variable inductor charging time, to reduce the pulse energy to levels suitable for smaller elements. It sometimes work - no guarantee

[Conrad Hoffman]

BTW, I believe one of the failure modes for NiMH cells is internal breakage. They are somewhat fragile and dropping them can be the end of them. Possibly newer ones are better in this regard.

[woody]

Thanks I just ordered a few 555 timers and I can probably find
the rest of the parts in my scrap pile