WHERE HAS ALL MY POWER GONE

I have checked and rechecked breakers on Gen. panel box and breakers GFI,s but what I didn't check was the house batteries until this am:.The inverter seems to power TV and floor outlet plus bath GFI and front storage compartment GFI which it is plug into but hard wired to coach. Just went out to check a little more still not finding any power but though just a chance to check house battery leads and water, one lead lose enough for the contact to move so I tightend. Went to inverter and seem to get a beep or two on tester so I went inside and TV tried to start but went off check inverter and it popped the 4 amp. fuse rest set and checked digital converter for tv and now has power. I hope batteries being low may have caused the trouble. I will let charge over nite and keep my fingers X. What I don't understand is there is a battery low red light on inverter and that didn't light and I guess I also don't understand exactly how inverters transfer power.