I think my two group 24 batteries have a charge capacity of about 80 amp-hours each. Costco, $80. There is a bit of a comparison here: http://www.lifelinebatteries.com/rvbatteries.php
Looks like you can get more capacity with a pair of 6 V batteries (note that energy capacity is actually in volt-amp-hours so multiply the amp hours by the voltage to compare them).
Like you, I find generators very noisy and smelly. Dear wife is afraid of CO. I got a bit of it as a little kid on a farm and another dose on a whale watching boat several years ago, and I get sick pretty quickly from exhaust smell. I can't use a generator so I've been just using engine charging and as little power as possible when boondocking. I have ordered a small 100 watt solar collector which I think will make a big difference for us. I think it will provide about 5 amps of battery charging, which is about what I get from the engine when driving only this will be right in the campsite, perfectly quiet, no smell and quite a few hours per day in the summer up here in the north.
I wouldn't be spending money on a rebuild for the old generator. I would put my money into solar or a new, quieter generator. The Honda seems to be the quietist but most expensive. Several others are pretty good on cost and noise.