I had a 2 bank mounted on the transom between the transom braces and screwed into the transom. I used a portable Minn Kota to top off my cranking battery. If it turns out that you have to get new batteries, go ahead and step up to 29s while you're at it. 31s would be better, but you'll need a sawzall and the jaws of life to get 'em in the G3.

I'm really thinking you've got one weak battery or that 2 amp charge is not bringing them to full state or your charger is toast.

I wouldn't be scared to buy a used, quality charger if you're on a budget.

Wannabe...