I got a Load Voltage checker from Tower to check batteries between flights. It's made by hobbico. If you get a volt meter I would make sure it checks under load. Another way if you don't have a load checker is to turn things on and move controls. Then turn off and check voltage. This should take care of any "surface voltage"

I found it is just easier to get the load volt meter.

Just my 2 cents.

P.S. I learned the hard way not to just take it off the charger and check voltage with a digital volt meter. The result was lost control midflight. This was after the battery read 5.2 volts as soon as it came off the charger. (I didn't have it plugged in more than 3 hours) And it was dead before this. The dang weather was perfect and I didn't use my head before leaving the house.

Del