My old diesel tractor wouldn't start the other day because the ancient
battery on it finally gave up the ghost.

I have a small car battery charger, but it is limited by the length of
its extension cord.

So, I'm wondering about several products:

1. The "combo" battery jump starter/charger devices I see around these
days. Don't know anything about them. Might be a good thing to have on a
boat, if you remember to keep its battery charged.

2. A really good battery charger, rejuvenator.

Suggestions?

Thanks!