I think a battery sufficient to realistically replace alternator output would be too large and expensive. Car alternator output is on the order of 1 to 2kW. A

I think a battery sufficient to realistically replace alternator output would be too large and expensive. Car alternator output is on the order of 1 to 2kW. A battery [1] which can do ~1kWh - 100A at 12V - is about $300 and weighs 12kg. It's also big - 40x20x25cm - stick it in your boot and you'll notice the space reduction. That would just do 1 hour, at the lowest level of alternator output. If you need more power or more range, double it; more of both, double it again. The next question to ask is do you trust keeping a $300 Chinese battery in your car without it blowing up? You probably want a reseller who'll stand behind their products, ensure the supply chain maintains quality, has sufficient safeguards, etc. The price is going to go up even more. [1] https://www.alibaba.com/product-detail/1KWH-Deep-Cycle-LiFePO4-12V-100Ah_60250913806.html https://www.alibaba.com/product-detail/1KWH-Deep-Cycle-LiFeP...