The IMA (integrated motor assist) has a normal 12v battery and an 144v battery, the motor is a 10KW and doubles as regeneration and alternator, it forms the flywheel of the car and can't be disconnected from the engine. Apparently the 144v will be used to start engine if sufficient charge in it otherwise the 12v is used.
If I did low mileage I would seriously look for a plugin hybrid or pure electric (although I am not a big fan really just being pragmatic, but the price would have to be right - I live in hope that as more are sold the price will plummet LOL ) - both will be expensive to buy but cheap to run, although with low mileage the payback period will run to decades, but will not deteriorate like an ICE car through standing idle for long periods as long as battery kept charged.