just turning on the radio and moving servos is NOT enough. nicads by nature give almost full power -right up until the moment they die! you need to use a ESV -Expanded Scale Voltmeter- lots of hobby companies make them- they are all over the place at swaps for about $5. field chargers can be used & there are several types-peak detection, constant volt types. as long as you do not charge at excessively high rates you will likely not damage your batteries. continued fast charging( complete charge in 15 min or so ) can cause venting as timing at this rate is very critical. you should still check with ESV. depending on the battery condition, type & # of servos 3-4 flights should be the minimum # . ive gotten 10 long flights on 3 channel planes easily - yes, it was ready for recharge.