800 commander

Hello. I'm new to this side by side stuff. Picking up a 2015 Commander 800 XT in a few days. One question I have that Google cannot answer is; what's the best for power in these machines?

When i turn my commander on the cluster throws a bunch of backwards Rs and wont crank. Its happened twice now and when i take the fuse out for the cluster it will crank. I took it to the dealer and they made an excuse up saying it was the battery weak but it doesnt make sense to me with the...