Unless you have tested the batery and know for SURE it's bad, check and clean the screw-in terminals at the battery--they're not like normal automotive battery terminals---they tend to loosen and because they're right where the rear tire dumps crap, they can short out and the also the terminals corrode. Some people have cut off the screw-in terminals and replaced them with standard automotive terminals--BUT you have make sure the your battery has posts.
The easiest way is to jump it and start it. Then raise the boom fully, remove the engine side panel, and possibly the side panel extension (if it has one) which guides and holds the lower portion of the engine side panel, then the battery. On my larger machine the battery is very heavy and is very awkward to lift. I use a box end wrench slipped over each battery post--when you lift the wrenches they grip the posts making it easier to lift it. My buddy who hasan LX665 said he didn't have any problems getting the battery out like I did.
I'm pretty sure you will have to lift the loader arms one way or another.