You need to run out and get a multimeter, they are inexpensive and can be purchased at Walmart. A multimeter should be supplied by the dealer that sells the RV. "Don't leave home without it!!!!"
Is this the same battery that died over winter, or a new one?
Is the battery hooked up properly? WHITE battery cable goes to FRAME GROUND, black goes to the TT's main 30 amp fuse?
The meter you are looking at is not connected to the TT's battery, it is connected to a wire that probably supplies power from the DC distribution frame to other things by the battery display (like the awning, slide out...)
What is the ACTUAL battery voltage of the battery (using a multimeter between the batteries POSITIVE and NEGATIVE terminals?
With Shore-power connected and without shore-power connected?
While disconnected, pull the 30 amp fuse and take a battery reading.
Also, check your battery cable connections. Are they clean and tight? One more place, check the the WHITE cable from the NEGATIVE battery terminal that connects to the FRAME ground bolt, and see if that is tight and clean.
Let us know what you find
RVing with SOLAR
2013 Jayco Eagle 284BHS
250Watt Grape Solar Panel, MorningStar MPPT 60 Charge Controller
1500 Watt Ramsond PSI, 2 Trojan T145 Batteries (260Ah)
2 - AirSight Wireless IP Cameras (used as rear view cameras)
EnGenius WI-FI extender, D-Link wireless (n) modem
MagicJack Internet Phone
2012 Ford F150XLT, EcoBoost w/3.73
157" Wheel base, HD Towing Package
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