How do I charge my 3 boat batteries with a DC to DC charger????

[McJensen]

Looking to charge my 3 AGM 12V boat batteries hooked up in series, 36 V total.

Load is a 36 V trolling motor.

Motor: 2006 250 Yamaha four stroke

Motor has AUX charging cable available - positive lead only, no negative.(???)

Boat is on trailer, so at home I charge batteries with a 3 bank 20 amp charger.

Question: how do I hook up a DC to DC charger using the motors AUX charging cable (positive only, no negative) to 3 AGM 12 V batteries hooked up in series for 36 V total.

 

[McJensen]

Add'l note - these 3 batteries are for the trolling motor only. I have 2 12 V batteries for starting & house use.

 

[Jasgeer]

I would be wary of charging three 12V AGM batteries in series without some form of BMS to keep each of the three batteries in balance. I know golf carts commonly do this but I am suggesting it may not be the best practice. I would be inclined to charge the three in a parallel circuit with one charger even though they are discharged in series. Or use separate 12V chargers around each of the batteries (this might be the cheapest solution).