Electric APU battery charging

Hi, I was wanting to get rid of the battery management system. Is there any reason to not simply charge the apu batteries by hooking the cables from the start batteries to apu batteries instead of first going to the battery separator ?
I use deep cycle batteries in apu. It does nothing much these days since ac unit died.
My truck constantly goes into low voltage mode . Set way too low I guess.
But my plan is to have 8 batteries so that don't happen. Then my fridge won't shut down every day when low voltage disconnect comes on.
That bms and separator are basically doing nothing as far as I can see.
Pu ls the terminals get dirty quick and then the bms trips and my APU batteries don't charge, it needs to go,

 

Im on it. I figured it would do no harm. I was worried that isolating them would cause overcharging of start batteries. Running down auxillary batteries would make the alternator charge but would also be charging the start batteries that would not need it . But then I do not run much of anything from my APU side. Use microwave when truck is running. my truck has the fridge on start battery system I think. So I figured 8 start batteries is better than 4. QUOTE="uncleal13, post: 12471218, member: 28026"]I had mine wired almost directly. I put an isolation switch to my auxiliary batteries. So while I was parked I shut off the switch so I didn’t drain the main truck batteries. Then in the morning after I started the truck I closed the switch to recharge the auxiliary batteries. Did that for six years.[/QUOTE]

 

Had two bad batteries. Start and auxillary. Both the one hooked to the BMS.
I just unhooked them and removed the start battery BMS, left on the other one.
3 batteries each side . Got no problems now.