This might be a dumb question but I'm wondering how often I should charge my NIMH batteries.

I have those ONYX chargers and all my batteries I use are NIMH for the starter boxes, glow igniters, and receivers.

I hate going out somewhere and finding my batteries almost dead but I don't want to charge them if they don't need it or over charge them.

I just plugged in one of my starter boxes and the screen said they had over 8 volts when the charging started. Is that too much to start charging?

I think the charger has a peak detector.

Back in the '80s, all we had was NICD and they had to be discharged first and then charged. I've been told I don't need to discharge NIMH first.

Or maybe my question is: When's the best time to charge these or does that even matter?

Charge before you plan to use them. Theres no need to discharge them. If they sit for a long time like a couple months then it may be a good idea to cycle them.