Standards-grade, free, no account — each one is the same engine that designs whole systems. Pick a tool, or design the whole build at once.
Ah and kWh you need from daily use, days and chemistry.
Recharge time, capped at what the bank actually accepts.
Ah per hour of driving — and the DC-DC size your alternator can handle.
How long a bank carries a given load.
Convert capacity so you can compare banks fairly.