2009 GEM e2

My name is Doug and I have a 2009 GEM. I put new Interstate Pro 29 marine batteries in vehicle in May 2013. Vehicle worked great all summer then this fall would get to 50% energy on indicator and then drop to 10% immediately.

Replaced two batteries that seemed the weakest. Problem still exists. Took to dealer–they did extensive testing, checked with Polaris and came back and told me I needed GEL batteries and that there was no other problem with the vehicle.

Any suggestions on what the problem might be?