It's not the most clear info but where did the OP say he didn't have lights?
He says the DC items are working fine, so likely not the DC side.
Also, the battery at 12.4v might indicate the battery charger is not getting 120v AC power as that should be up around 12.7v (higher if the battery charger is actively charging). Battery isn't dead but it might not be charging.
Do any of the outlets have power (not all may be on GFCI)? Try pulling the GFCI outlet and test the wires feeding it to see if it has 120v power.
- Yes, it's probably GFCI related
- No, work your way back upstream towards the panel until you find 120v power and that should narrow down the issue.
- I'm guessing not GFCI as it won't take out everything 120v.
If you need more help, tell us what items are and are not working as that will help narrow down possibilities.