There is probably not much that will drain your battery in your
Boler except possibly if your
fridge was on 12V.......recharge your battery and then after a while, give it time to dissipate any gas from the charging otherwise it could blow up, hook up your one cable and touch the other cable to the other battery post or run about a 2 ft jumper from the post and arc that to your disconnected cable away from the battery, and see if you get any spark between the post and cable......if you do, start disconnecting anything that may be drawing current and trying for spark each time until there is no more arcing....or for safety, you could also put a small 12V bulb or test
light in series between the wire and battery and if it
lights, you`ve got something draining the current....many ways to test but I find these the easiest.....Sometimes batteries can test good and then later dead short inside and you`ll get zero for power....Benny