What's the best trickle charger?

My Toyota Proace is not used very often resulting in the battery draining down. Will a solar powered trickle charger keep the battery topped up? I am considering a model with EOPD plug as i understand...

Can storing a hybrid for several months damage the batteries?

My son is thinking of buying a Toyota Yaris Cross which may be left in storage for some months at a time. No electric supply will be available. Can this damage the drive battery or accessory battery?

Can I buy a car with solar panels?

Why don't manufacturers omit the sunroof and add solar panels instead? They could be used to power the obligatory air con and the sound systems and eventually trickle charge the main batteries to charge...