Q’s for DIY dual battery guys


Active member
Local time
4:46 AM
Apr 21, 2024
I am considering adding a second battery for longer trips.
The bike is a Magicycle Deer 72v 20ah.
My long trips will be with a trailer so what I would like to do is add a huge (like 72v 50ah) battery under the luggage rack on the trailer.
Might I be better off getting multiple of the same battery that is currently on the bike for the convenience of a battery rotation?
I haven’t opened up the covers yet to see what the existing battery connections are yet. Yes I know, that is pretty much a first step.
I *assume* I will need to add a dual battery discharge adapter to the bike, as well as wiring to the trailer.
What I am not finding on the net is specifics on how the dual discharge adapters work.
Can I use a second battery of different capacity with the adapter (20ah + 50ah)? Will the adapter pull current from the stronger battery?
Do the batteries need to be at similar charge levels even with the adapter?

If I do use the same battery as the bike do these look like a common battery so I will be able to find/get slider battery mounts for the trailer?
I know these spare batteries are only 15ah but they were 1/4 the cost of 20ah spares.