12V - Run #2 starter battery with deep cycle battery in parallel?

[MET45]

I converted a modular ambulance on a 2015 E-350 Super Duty cutaway, V-10, with a 225 amp alternator.

This is the ambulance Battery 1, under the hood.


This is Battery # 2 in the side compartment. Both Battery 1 and 2 are starter lead acid/gel batteries. Battery #2 is also connected to a 3K watt inverter and powers some low amp electronics, a fan, and 12V fridge off and on.



This Isolator is in the rear electrical panel. I believe it isolated Battery 1 from Battery 2.


This is my new Battery #3, Renogy 200Ah AGM.



I plan to fully charge and balance this battery with Battery # 2, and connect them in parallel with 2AWG, 2 gauge cables.

I plan to charge all 3 off the alternator when driving, charge off 15 amp smart charger when camped with shoreline, or with 200 Watt panels and charge controller when camped.

From what I have researched, although it is not optimal for any of the Batteries, it should not be unsafe and batteries should level out and charge/discharge evenly. I know it is optimal to have 2 separate systems, but I wanted to utilize some of the existing wiring and systems.

I would appreciate any advice or opinion from you 12 volt battery wizards, or someone who has run starter and deep cycle batteries in parallel before.

 

[MET45]

 

[Harley]

Both old batteries are flooded, not gel. Im not so sure it would be recommended combining lead cell with AGMs. Might want to look into that aspect more. Ive never seen or heard of anybody mix matching batteries like that on the same system. 🤷‍♂️

 

[Smokers10x]

I've built a few off-grid, backup solar power stations. I have one in my garage and a few in my back yard. I use Renogy solar charge controllers that have a bluetooth module and a smart phone app. All of my batteries are12v Lithium Iron Phosphate (LiFePO4). My garage system is 24v. 1040w of solar, 480 amp hour battery bank, 40 amp solar charger controller, 2000w pure sine wave inverter.

It is not ideal to use a starter battery to power an inverter. You should use the Renogy deep cycle battery with the inverter.

I'm not familiar with your application, but I think you need a DC to DC charger. Alternators are not really designed for what you want to do. Renogy makes one, but not sure how to wire it up. I've included a link to a DIY solar forum that can help answer your question.

Safe to Power a DC to DC charger *Directly* via Alternator?https://diysolarforum.com/threads/safe-to-power-a-dc-to-dc-charger-directly-via-alternator.55195/

Here's a link to Renogy DC-DC chargers on Amazon.
https://www.amazon.com/s?k=renogy+d...x=renogy+dc,aps,183&ref=nb_sb_ss_ts-doa-p_1_9