Trouble charging lithium camper battery

Victron monitor shows 100% capacity but only 11.3 volts.
Any ideas ?
Do I need to reset the monitor somehow? Camper has not been used for some time.

Reset SoC manually to 0%, charge battery until bmv synchronizes to 100% again.

Your BMV settings may well be wrong, especially your charged voltage. Have a read of this FAQ for solving high SOC at low voltage.

https://community.victronenergy.com/t/shunt-battery-monitor-jumping-to-100-or-reporting-a-high-soc-when-the-volts-are-low-and-or-the-bms-has-disconnected/88