Body Bagger has it right. As a mechanic first, and a weldor second, I know my way round the new ones as well as the old stuff. This however is classic.

Take your battery terminals, and look at them, white and fuzzy is bad. Green is also really bad. Get a wire brush, take all of the white fuzzy stuff off, and re connect. Make sure that the ground is connected somewhere that there is a good connection...even if your battery connections are great, you need that good ground for anything to support the current. Make sure any connections are tight, loose connections take more current to cross, and that means less for your starter to use. After you finish cleaning and re connecting everything though, go ahead and put some vaseline on those connections to help protect them from future issue.

AFTER you take care of those issues if they exist, then go ahead and check your battery. You can probably take it to a local autozone, or napa, and have it load tested. If it fails that, regardless of voltage that it holds, replace it.

I cant tell you how many times I've overlooked the easier option first...just because I thought, "oh, that cant be the issue...thatd be WAY too simple!" 2 hours later, and frustrated, I came to find it WAS the simple option.