Mike4 wrote:1) It takes about 8 hours to fully charge a lead acid battery from 50% state of charge using an appropriately sized charger, e.g. the car alternator
https://batteryuniversity.com/learn/art ... id_battery
OK - A car battery, fully charged has around 45 ampere hours capacity. So a half-charge will be about 24 ampere hours - or about 3 amps over 8 hours. A modest home charger should accomplish this. But a modern car's alternator is usually capable of supplying 60 amps or more. So about half an hours driving should suffice - and it would be a better idea than leaving it idling on the driveway..