There are some more powerful batteries that will fit our battery box. I haven't tried one yet, but when my Deka battery needs replacing again (in a few years!) I might try one of the "bigger" batterys. Here's some info I picked up when I was looking at replacing the battery on my '09.
I'm using a Deka battery made by East Penn Mfg. Their replacement for the standard Yuasa YTX9-BS is the ETX9.
I haven't tried it myself but I have found out that there are three Yuasa Batteries that are almost exactly the same physical size, but more Amp Hours/Cold Cranking Amps. I was really tempted to try one in my '09 when I replaced the battery this spring, but ended up going with the Deka.
The stock YTX9-BS-BS is 150x87x105 mm and 8AH/120CCA
The YTX-12A-BS is an AGM battery with the same dimensions and 9.5AH/175CCA
The YTZ 12S is an AGM battery that is 150x87x110 (5mm taller) and 11AH/210CCA
The YTZ 14S is an AGM battery that is also 150x87x110 and packs 11.2AH and 230CCA
I went to pick up 2 of the YTZ14S for me and my riding buddy and when tested one of the only two in stock had a bad cell. That made me uneasy, so I had him bring out a Deka ETX9 and test it and it exceeded the CCA of the YTZ14S so I bought the American made Dekka this time. (the salesperson told me Deka is known to be conservative in rating their batteries) I'd still like to do a side by side comparison of the YTZ battery and see if it spins the DR any better, but I've always had good service from the Dekka, so I'm not sure if I'll switch next time or not.
It sure looks like the YTZ14S might be an interesting replacement for the YTX9. It;s only 3/16" taller (5mm) and with a couple of washers under the battery retainer it apparantly fits under the seat just fine. However, if you are really concerned about weight, it does weigh about 2 pounds more than the stocker.
The only concern I might have is that there are probably more plates in the higher capacity battary in the same (relatively) size package. I've read before that this could cause a problem due to the plates being closer together.
Having said all that, I'm REALLY satisfied with the Deka ETX9. Also made in the U.S. of A. if that matters to you.
I can't take credit for this. Here's the article I found this info in and a big THANK YOU to "Scott", wherever you are!