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batteries - rechargable - charge rate on batteries with lost capacity?

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lee321987

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When batteries have a lower capacity then they are rated, is it still okay to base your charge rate on their rated capacity?

EXAMPLE:
I have some 2000mAh AA NIMH that my battery analyzer says only have ~1000mAh capacity.
Is it okay to consider C to be 2AMPs, or should I use C=1AMP when calculating charge rate?

(I've read that NIMH's that are this depleted should be thrown away, but I only use these in my mouse, and they last for a long time in there)
 

KerimF

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In my opinion, when a battery gets old, it won't matter a lot if the charge algorithm is optimum or not.
On the other hand, charging at a lower rate is usually better to get more efficient charging capacity though the price is time.
Sometimes (not recommended without tests) pulsed charging current with a relatively high value (as a temporarily refresh) may help restore a part of the lost capacity though this depends on the battery type.

OT: May I ask you if your battery analyser measure also its internal resistance (impedance)?

Kerim
 

lee321987

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Perhaps I should have worded my question better.
I'd like to know if charging a 2000mAh-rated battery that only has an actual capacity of 1000mAh at 2AMPs has the same negative effect as charging a brand new 1000mAh-rated battery at 2AMPs.

About the pulsing - yes, I've brought some life back into a few NIMH and NiCad's by charging a 70,000MFD capacitor (size of a soda can) with a 12volt wall-wart, and discharging it through the batteries...

About the battery analyzer - yes it measures impedance (on at least one of it's charging algorithms), but never displays this number. The model is MH-C9000 by Powerex.
 

KerimF

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Logically an old 1000mAH battery is somehow equivalent, in respect to capacity, to a fresh 1000mAH one. That is for an old battery, both the charging and discharging currents need to be lowered (if they were relatively high) to extent further its useful life to a good extent.
This may explain the relatively fast degradation of the battery capacity if the fast charging algorithm is kept the same along its life (the same applies if the load is rather heavy).
Fortunately, the battery prices are going down so that replacing it once a year won't be a problem though I will be more pleased if it lasts for 5 years instead :)

Kerim
 

lee321987

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@KerimF
I assumed I should lower the charge rate on a depleted-capacity battery, but I don't know exactly how the chemistry works, so I wasn't sure.
I'm guessing you're right.
 

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