Transit custom 2020 battery help

[bm_99]

People my lovely 20 plate van has started giving some issues now

Fuel gauge is showing as 1/4 left but computer is saying 1 mile only. Topped up £15 (only Shell nearby) and gauge went up and so did the computer - now showing 120 miles left

Have had to crank twice sometimes to start the van, then on sat nothing. Called aa and they said more than likely new battery. Was reading 10v on sat
This morning reading 11.99 and haven't driven since sat and this evening nothing not starting at all and batt showing at 11.6v

Any thoughts plz

[unofix]

Either put the battery on charge for at least 12 hours but more likely 24, or get a new battery fitted.

[bm_99]

Checked with my battery tester and 10.4ish volts coming from the battery itself
Will.try and pickup new battery from Halfords tomorrow sometime as with tradecard it's cheaper than euros