Obviously another important part of an EV.
Almost all electric vehicles have one battery charger that charges the entire battery pack in series. For example, my EV will have a 72V system voltage, so the "normal" thing to do would be to use a 72V battery charger. However, this way of charging only works if all of your batteries are in the same condition. If you attempt to series charge batteries that are not equal, the weaker ones will reach full charge first and then overcharge when the stronger ones catch up. The result is an unbalanced (aka weak and failure prone) battery pack.
Battery balancers can be used. Simple balancers basically shunt charging current around "full" batteries, allowing all the batteries to charge evenly. But those cost money and are not in the budget.
My solution? Individual 12V chargers. Six of them, because 6 X12 = 72V which will be my system voltage.
They are supposedly smart chargers, so they shut off automatically when a battery is fully charged, and they charge at 10 amps. I have been using one of them to keep my entire battery pack alive in the garage with a 2A charge.
So I will use 12 batteries in the car - six "buddy" parallel pairs in series to get 72V. Each charger will be responsible for charging one of these buddy pairs, so two batteries. Makes sense?