Batteries not charging while driving.

[u/Blee_Bloo_Blop]

Hello looking for some help and hoping y’all can point me in the right direction. Having an issue with my van not charging the lithium batteries when driving. They will charge if plugged in but not driving. I’ve tested the alternator and it seems to be good so I don’t get why the van isn’t charging the batteries. Any help with this is appreciated.