> I know there are 28V Li-ion tool chargers but I don't think
> they would work for lead acid.
Are you sure they are lead-acid ? The ones my helicopter pilot buddy used
to give me were nickel-cadmium.
FWIW, some APC UPS units at least used to have external battery connections.
Even if you had to modify the charger portion somewhat for a different
battery voltage/chemistry, I would think a used UPS would be a much cheaper
starting point than trying to source the components (and design) to build
your own from scratch.
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