I wouldn't necessarily cycle them. My glow and gas models all have NiMH receiver packs and I keep the most flown packs on a timed powerstrip that puts one hour of charge in them every day. That way they're always ready to go. Every few months if a pack hasn't been used i cycle it.

I your example I would charge for a couple hours before going to the field if it's a 60 to 100mAh wall wart. If it's a more powerful charger you can zap it for 15 minutes - or if 12v charge it up on the way to the field.

You got the right idea - believe the voltmeter.