battery problem?
 

so i finnally broke down and bought some rechargable NiMh AA for my radio- some ProTek SKATES, 2500mah

im charging them @ .5a with a delta peak of 5mv and they'll charge to about 11.9v- they get pretty hot too - my tempcutoff is at 120deg and they get close...

im asking because when i was using normal, non rechargeable AA - a new set would start me off at 12.9v and seem to last allot longer than these new ones i got- ive only charged the new ones twice...

???

New batteries need to be cycled (charged/discharged) a few times to kinda "break 'em in". They'll start lasting longer after a few cycles.

Rechargeables have a nominal voltage of 1.2V per cell whereas alkalines have a nominal voltage of 1.5V per cell. That's why your old batteries had a higher combined voltage.

What seems a little strange is that they're getting so warm when only charged at .5A.

regular alkaline AA's are 1.5 volt per cell and rechargeables are 1.2 volt per cell. The rechargeable should peak at about 11.2 -11.5 volts and will probably drop to about 10.8 within a short time of use but should stay above ten volts for a long time. Try cycling the pack a few times if it is not lasting very long. I usually just charge mine before each race day and mine generally last til the next race day.

:rolleyes: I gotta learn to type faster LOL

I have used a lot of rechargeable AA mostly in my digicams, but also for rc and they def take a while to indicate what they will really perform like. I've had some that took as many as 10cycles before they settled down and quit changing. The unknown in all these are how long its been since they were manufactured. That temp is normal for the internal reaction during charging - up to 130F is considered normal.

If you want to, just cycle them in a charger, watch the numbers and when they stop changing more than 10% between charges, that's about as good as they're going to get.

i used to run rechargeable batts in my radio but i finally got a lipo instead... the bad thing about the the rechargeable batts over the regulars is once they get low they drop of really really fast..

i never noticed alkis are 1.5v- that explains the voltage difference... and like you said mine are topping off at 11.8ish and then drop slightly so i guess they are probably fine. from what ive read ishould discharge them to .9v/cell so 7.2v for 8 cells? - and at what discharge rate?

Yes, discharge would be to 7.2v for 8 cells. They may be getting warm b/c of your peak detect, for small cells I generally use 3mv/cell. You should also be able to charge those cells at 1 mah at least.