vanilla ice
1 MW
Are you sure your original drawring is correct? Looks like you are reverse charging a single battery in that one. Make sure your polarity is correct on the charge socket.
This should be it..

I similarly added an extra bat in series to my Currie, but when I charge it with the stock 24v charger I rewire it back to stock, the use a separate 12v charger on the 3rd brick.
This should be it..

I similarly added an extra bat in series to my Currie, but when I charge it with the stock 24v charger I rewire it back to stock, the use a separate 12v charger on the 3rd brick.