How can I check to see if my alternator is charging my engine batteries. I just got lithium house batteries and the BIM they installed charges 15 min on and 15 minutes off. And my engine batter is loosing volts. So I'm not sure if it's this new BIM or the alternator.
Rick
Find out if they wired the new BIM to charge the engine batteries,with the engine running the alternator should be charging your engine batteries at somewhere around 13.7 volts,some of us use a trickle charger to charge the engine batteries.
The BIM on your house batteries should be totally independent of your engine batteries. The "15 min charging" sounds like they installed something similar to a LiFePO4 Battery Isolation Manager - Battle Born Batteries (https://battlebornbatteries.com/shop/lifepo4-battery-isolation-manager/) . If installed properly, it should shut down charging from the alternator to the house batteries every 20 minutes but should not affect the engine battery charging.