# Batteries getting over charged?

My team has recently noticed that the vex batteries, used for the brain and power expander, are getting charged up to even 8.4 volts with the vex “smart chargers”.
Or are the batteries just old?
What can we do to fix this?
Are there any ways we can de-charge the batteries?
Would over charged batteries cause the motors to wear out quicker?

What did they normally charge to? Ours always charge up to at least 8.1v…

We find that by the time they hit 7.2v, they act like they’re empty…

//Andrew

they should only charge to about 7.5 MAX but lately they have been atleast 8. With them over charging, EasyC and the cortex says its dead when it is slightly over 7.2 volts.

We’ve always seen them charge to at least 8v, and return dead at 7.2v. Where did you find the 7.5v maximum number?

//Andrew

the VEX batteries are the same as normal Rc car batteries and that is where they should be.

Hmmm… I don’t know what help I can give, then. I know I’m now curious about this now, and will probably end up asking someone from VEX at the tourney.

//Andrew

I think it’s supposed to do that; When you read the batteries, it has a different voltage when it’s being used by a motor and when you just test it with a multimeter. This is why we once rigged up a device to measure the working voltage when the battery is attached to a drill. But if you know that 8.4 is charged and 7.5 is dead when you measure it the same way, then it really doesn’t matter.

Good o’l V=IR.

The internal resistance of the battery makes the measured voltage look lower when it’s supplying electricity.

Our batteries always charge to about 8.5, although im fairly certain we’ve gotten them past 9. Lol

Our fully charged batteries are usually ~8.5V on the multimeter, but we’ve had them go past 9 at times. Usually we switch them between the range of 7.2 and 7.7 depending on how fast we notice the performance decrease in the robot.