I've got essentially the same battery. That charger is pretty good. It's best not to run the battery all the way down too often, though with NiMH it's not as big a sin as it is with LiIon. I think good rule of thumb advice these days is to leave whatever battery you have floating somewhere in the middle of its charge range as much as possible. Charge it before it gets drained too low, but also don't top it up and then leave it sit for a week on a regular basis.

If you're riding tomorrow and it's at 50% charge, top it up overnight. If it's at 50% and you won't ride until Monday, top it up Sunday night. If it's at 80% charge and you're only drawing 20% out per ride, I'd just use it as is for a couple of rides, charging it up at around 40%.

The big danger is getting cell voltage down to 0.95 volts or lower. Any time you run a pack down to maybe 10% of its charge left, you run the risk that ONE cell in there is not quite as good as the rest, and you're going to hammer it into the ground. That's why it's best not to run the pack really low very often.

I think it's a good idea to charge overnight too, so that the pack sits on trickle charge for several hours. That way, if there's one or two weaker cells in the pack (they'll tend to be the last ones to get fully charged) they'll get properly topped off in the time on trickle charge, whereas if you took the pack off as soon as the light turned green, that one or two cells may not actually be fully charged. The charger looks for an overall dip in the charge voltage to know when to stop, and with 12 cells in series, if 10 of them top off close together but two aren't charged yet, there would still be an overall voltage drop and the charger will probably stop.