1C means if it's a 4000mah battery, charge it at 4A max. If it's a 1600mah battery, charge it at 1.6A max
NiMH Batteries will usually get pretty hot in the last 500mah of charging, that's normal. My 7.2v 4200mah battery gets so hot you almost can't hold it, but it's done that for years and still holds 4200mah.
Also, when your firing, stock gun wiring will heat up pretty fast because of the resistance in it, more resistance = more heat. Your battery shouldn't get too hot unless your firing alot
And if you don't like hot batteries, buy a LiPo, they never heat up!