Rechargable Batteries

[SomeSaba]

Hello, i have two 9.6v rechargable batteries, one is Ni-Cd and the other Ni-MH. I also have a 6 cell Ni-MH as well.

On my robot, i cannot exceed 9.6Volts due to the competition's voltage restrictions. If i charge my 7.2V batteries, they will be about 8.5-8.0volts, if i charge the 9.6V batteries they tend to be anywhere from 11-10.1volts. Am i over-charging them or is +/- ~1volt common for rechargables?

I really want to hit 9.6Volts exactly or at least close. So is it an over-charging problem or what? The 7.2Volt battery is brand new, but my 9.6V ones are 4 years old  . Also I'm only charging them for ~2 hours. 

Thanks for any replies!

[Hal9000]

I think you should just say to the judges, "Look at the batteries.......as you probably know, they won't stay at 11 volts for very long, plus, the batteries actually state they are 9.6V"

Surely they cannot argue with that.

[Admin]

a competition i once went to didnt have any voltage limits, but instead a cell count and cell size limit. for example, i couldnt have more than 5 cells of type C. to have a voltage requirement can be somewhat ambiguous, as you noticed.

batteries are actually rarely at the rated voltage. at full charge, it could be ~20% higher, and at full drain perhaps ~20% below. if they say 9.6V, I would assume they mean the voltage rating, and not the actual measured voltage. a 9.6V will be allowed.

if your battery is 4 years old, consider getting a new one. the older batteries arent nearly as good, and if you didnt take good care of your NiCad, it might not be so good anyway.