I have an automatic 2003 Eiger 2x4 and the battery does not stay charged. In fact, even when you have riden all day and start it up frequently, the battery will still lose its charge. We have went through several batteries, now we have two we alternate and keep a battery charger handy.

Has anyone encountered this problem? Got any suggestions regarding the cause?

 

Sounds like you've got a slow drain somewhere in your system. Turn the key off on the bike and use a 12v automotive test light. Place it in series w/ the negative battery cable (ie. disconnect negative battery cable and connect one end to test light wire and touch test light to the negative terminal. If the light lights up you've got something draining. Then proceed to remove fuses one by one until the light goes out. Then you know where the suspect circuit is. If you're going to be going through all this go buy a service manual since they have full wiring schematics.
Do you have a winch, or any other accessories, chech those first.