Julian46, we have many posts on this topic.
Simply put, leave your main pack at around six bars (around 40%) and, if possible, attach a small smart 'float' charger (e.g. Battery Tender) to your 12v battery.
The reason for keeping the 12v battery on a charger is because there is a continuous low power draw (e.g., from the i-MiEV alarm system) which will easily run down our now older 12v batteries.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV