# Recharging on an NiMh "Dumb" Timer-based Charger - Termination Voltage?

Right now I only have "dumb" timer-based chargers for charging my AA & AAA NiMh cells. I did a little searching on charging NiMh cells and it seems 1.4 to 1.5 is the voltage for a fully charged cell. Using these chargers, would I be ok to just occasionally pull cells off the charger and check their voltage with a DMM until I see about 1.45v? (I've never known about charger termination voltages until I encountered Li-Ion cells, so I am figuring NiMh are the same way - reach a voltage where the charge should be terminated.)

This is what I have been doing (have two different chargers running charging up 8 AA's (non-LSD type) - both at 360mA. The one set of cells came up to 1.40v and so I've left them on looking for 1.45v. I think it's been about 1 hour since I read 1.4v and they are just now up to 1.42v. Do you think they are done?

Thanks,
Garry

State of charge of NiMH batteries isn't determined by voltage, like the case is with Lithium chemistries (Li-Ion, Li-Polymer, LiFePO4, LiMn etc). Timer-based chargers should charge at 0.1C for 16 hours, if I remember correctly. As long as battery is nearly-empty when you put it in that type of charger, it'll charge up fine.

Well that's just it, they weren't really empty (well not all of them). I just wanted to know a way to know they are fully charged and not just let them "cook" due to the timer.

-Garry

You mean 0.1 Ah (100 mah) ?

Nope, C (some manufacturers like Panasonic use “lt” for measuring of same thing). C = Capacity/current, so for battery with e.g. 4200mAh, 0.1C = 420mA.

Btw Ah & mAh refer to capacity, not current (1 Ampere*hour means battery can provide 1 ampere for 1 hour (or 0.01 ampere for 100 hours et cetera)).

A charged Nimh should reach up to 1.42v, that is normal.

Thanks Kokopelli.

-Garry

...

NiMH (and NiCd) doesn't really have a defined end voltage. What chargers do is detect the voltage is not rising any more, or that the cells heat up. (Basically the same thing as the heat will depress the voltage it seems).

This also is the reason these cells cannot be left on float charge.