I have a trainer that I just bought a 4.8V/1650 millamp battery for. Question: It says to charge for 16-18 hours. If I leave it charged longer than that, will it hurt it? Same with Futaba transmitter batttery, will it hurt it to charge it a long time?

I'm not an expert on this, but in general you take the mah of the battery & charge it at 1/10 of that for about 12 hours.

For example if you have a 1000 mah battery & your charger is a 100mah charger then theoretically it would charge it in 10 hours, but there's inefficiencies so you tack on a few extra hours.

I just bought a 2000 mah battery and I am charging it initially at 100mah for about 24 hours to give it a slow charge. After I cycle through it a couple times I'll charge it at 200mah which should take about 10-12 hours.

I read that you can safely leave a 25mah charger on for long periods of time, but I think a 100mah would damage the battery after an extended period of time. I have always charged mine for 12 hours prior to flight & never left them plugged in for a long time. I'm sure the more experienced on this board can give you better advice.

Whenever I have questions about battery charging, I go to Red's RC Battery Clinic: http://www.rcbatteryclinic.com/ . Lots of information from an expert.

I second reading up on it at the RCbattery clinic.

If you are using a wall wart charger you will need to charge for 14-16 hours before flying. While it's not recommended you can leave it on longer than that with no problems. Lots of people have forgotten them and left them on for days or weeks with no problems, but you are better off by taking them off the charger after the charge time is over

Ken

If your new battery is a NIMH, then you have to charge it at .10 of its rated capacity. If you are using the wall wart that came with your radio, you will never reach full capacity of the battery and risk damaging it.

I have to dissagree with mscic-RCU. As long as your charger is putting out more current than the self discharge current is, you will eventually reach a full charge. It is just plain logic, if you put energy in it must do something, either charge the battery or raise the temperature of the battery. That is why batteries get warm or, in some cases hot, at the end of charge. The excess energy, once the chemical action has reached its saturation point, results in heat due to the recombination of elements at the positive terminal. Plain old physics and chemistry.