IMO your first priority should be to figure out what's going on with the battery and/or charging system. Do you have a digital multi meter? If so, it's a very easy thing to verify that the non-load voltage is around 12.5V and also that loading it up will maintain one steady value somewhere in the range of 13.0-14.5V. There is also another test that you can do with the MM to see if there is a vampire draw happening, beyond the amount that is normal and expected.