Orion XS charging trolling motor lifepo

DIY
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1

Hi everyone,
i have a small boat with Mercury 80 (2020) which has 35 amp alternator. Currently, only one 100ah AGM battery is used for start and to power all loads, which are not significant (lights, chartplotter…). Smart shunt is connected to it in order to monitor it.

Now, I’m planning to install bow trolling motor which will be run by 100ah lifepo4 battery, which will be completely independent of all other loads with only purpose to run trolling motor when fishing.
Since there is no space for solar panels, no shore power, only way to charge lithium battery will be through dc to dc charger. Because of smaller size, it’s ability to be configured, and not getting too hot as others, my plan is to install Orion XS 50, and limit it to 15amps in order to not push too much load to alternator.

I need help with wiring. Plan is to connect input and ground from AGM starter battery (no shared ground between AGM and Lithium), and output to lithium. Is it going to work properly like this

Thank you

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2

Unfortunately no, the XS is a non-isolated charger, which means it requires a common negative return path between both batteries - they must share a ground, without exception.

3

And the ground connection has to be rated for the charge current you are going to use, same gauge as the positive Orion cables.