I just got back in to rc I have a new on road the battery is a 7.4 v 3900 25 c lipo what do I put the charger to also I have my rc dirt bike battery is 3 cell 11.1 v 4000

You should be safe if you charge at 1C, to determine 1C for a battery divide the Mah rating by 1000. For your the 7.4V battery charge at 3.9amp, the 11.1 volt charge at 4amp. Also ensure voltages are set correctly and you are balance charging.