The following pages describe using a 12V charger to automatically charge pack batteries one at a time, instead of all at once in series. It will only work if you are not in a hurry to charge your pack.

The point is this: use one 12V charger to charge any number of batteries. You could do the same thing by charging one battery, and when it's done, manually moving the charger to the next battery. The idea behind this is to automate that process. If you have a 48V pack why not just buy a 48V charger? If that's your main vehicle and you're not changing the pack size, sure. But I had a 48V motorcycle, and now I'm working on a 36V scooter.

The main expense for the project is the 12V charger, and some 30A automotive relays.

*Disclaimer - this system switches the charger between batteries using a timer. A far better system would switch when the battery is actually charged (possibly triggered by the charger itself?). When I have some time I'd like to build it. If you build it let me know.