Need some help with DC issue

[Paul T]

I discovered that my 12v system shuts down when shore power goes off. The inverter codes are low battery but the problem is that the batteries are running at about 13.5 volts. I see the power at the battery terminals but still no 12v. The path is from the batteries to a circuit breaker, which was not tripped to a buss fuse (I think) to the transfer switch to the inverter. I get nothing from the circuit breaker forward but then again I’m not to well versed with using one other than to check ac and dc voltage. Any suggestions would be helpful. Thanks.