If it is a receiver pack in a Nitro, charge it as low as you can when you're at home. At the track,charge it at 0.5 amps. You don't need power out of these batteries, you want life between charges.

When I was using NiMh receiver packs I would take them home and charge them at 0.1 amps. Then I would discharge them at the same. That get's a nice deep cycle into them. The I try to only charge at 0.5 amps from then on in. I would bump it to 1 amp if I needed the pack charged sooner though.