Sea Level Monitor of Batteries

[Hwerb]

I have a 2024 Flying Cloud 25FBT with 2 x 100 amp hour Battle Born LiFePO batteries and solar panels. It has just survived the winter in Bel Air, MD. As a part of winterizing my travel trailer, I unhooked the negative on the batteries in early December. Upon reattaching the negative in March and waking the batteries up, I noticed the Sea Level Monitor was registering the battery voltage at zero. However, the readout on my Victron monitor indicated 13.9V.

Can you tell me what is going on and how I can fix the problem?

[TitusNW]

Use/Store Battery Guard Intellitec relay engaged?
Steve