A fair rule (not a "hard" rule) is never to dip below the packs baseline voltage and you will be fine. 4.8 volt pack, stop at 4.8. A 6 volt pack, stop at 6v. This applies pretty much only to nicad and nimh only. You can dip a couple of tenths under the baseline voltage and not get in trouble but why push it?

I use 1.5 and 2 amp loads when I test my stuff, but that's with Lithions. A one amp load should be the minimum load with larger stuff, imo.