I am wanting to DC-DC charge a gen2 foil drive battery from a 12v Battery on the boat. I have the Icharger dx12 that can handle a 11s battery from a 12v power source. When I connect the battery it is telling me that a balance connection is required. Do I need to be doing anything with the center pins on the xt90i connector or any way to bypass balance on this charger or recommendations for another charger that would work directly? Planning to charge at the same 4A as the foil drive charger but worried about damaging the BMS.
It’s is essential that you charge via the center pin - otherwise you will be bypassing the BMS and things will go wrong eventually 
Grab a multi meter and measure what the original charger is doing on its pins and match it with your new charger.
Pretty sure the center pins (both) are negative to the BMS.
But tread carefully, especially on a boat!
Hey @xraydoc - curious if you made any progress here. I’m hoping to do something similar (but using an off-brand AC charger, not a boat battery), but I’m struggling to reverse engineer the XT90i plug on the Gen2 charger. Here’s what I’ve found so far.
- There are only 2 wires (red & blk) from the charging cable wired to the inside of the FD charger.
- Yet the other end of the charging cable has 4 pins in the Xt90i - a large pair and a small pair. Both pair are required. If you connect only the large or only the small pair to the battery, it won’t charge.
- This suggests to me that something hidden is going inside the Xt90 plug end of the charging cable. A continuity test between the 2 small plugs failed, so it’s doing more than a simple loopback to the battery, yet it seems too small to have much additional circuitry going on in the plug alone.
That’s about as far as I have gotten and my experience with battery chargers is limited.
1 Like
The charger is only wired to the main positive on the connector and the negative is too one of the smaller pins. You can usually see if it’s to the top or bottom one just by looking. You do not use the main negative at all for charging. The small pin is wired directly to the BMS on the battery side. Here is a very crude quick drawing, but hopefully it helps.
1 Like
Thank you! Very helpful.