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Here's a pretty interesting way to charge a lot of batteries with just one charger, Kalikast writes - "The following pages describe using relays with a high-current adjustable 13.5/15V power supply to automatically charge EV batteries one at a time, instead of concurrently in series. It will only work if you are not in a hurry to charge your pack. The advantage is charging with a less expensive power source, in this case an SP-500-13.5 36A supply, which cost about $325 Canadian at the time. There is no reason you couldn't use a less expensive supply - or if you have some way to limit the charging current. The next most expensive piece is the 30A relays, which cost about $4 each. " [via] - Link.