I bought mine from
Batteries +, they were a little higher amp hour rating (235AH) than the interstates at Costco and a little cheaper with a 10% online purchase, in store pick up coupon, which I believe they still offer.
I also had to buy a new battery box, since the GC2 are taller than the G24.
I have a battery water filling system, that I bought on amazon, that sounds like the one Sourdough has, drop the hose into a bottle of distilled water and squeeze the pump ball until it won't squeeze any more... love it.
The new converter I bought at the same time is a 4 stage unit and I leave the trailer plugged in all the time at home.
-Brian