Having battery issues with my ’13 sportsman 500

So my last two rides I’ve had some issues with my battery. It is the original battery I think so may be due for a new one but I still think it’s good. The four wheeler runs great and has no issues until late in the ride and after the battery gets mud slung all over it and then I’ll have to get it jumped off every now and then. I think that’s what is causing the issues cause once I get it home and hose it off it runs fine. Is there any kind of covering I can buy for the battery to help keep the mud off it? Kind of a dumb location for it right on top of the back left wheel under the fender.