Adding Solar (and Batteries?) To Existing System

[willis102]

Hey Guys!

I recently bought a truck that came prewired with an electrical system. The truck was built by an ambulance manufacturer (although it wasn't an ambulance) and I was able to get a copy of the wiring schematic from them. Here's the battery / charging system section of the schematic:



This is a little complicated, but, ideally, I'd like to use it as a starting point to add components to / remove components from instead of starting over. I have no experience designing or building solar power systems, so forgive any dumb ideas or questions that follow!

I'd like to add solar and additional battery capacity. Presently, the batteries are as follows:

BATT 1 is a Motorcraft BXT-65-750 (I believe that's a lead acid battery)
BATT 2 is disconnected (no battery when I bought it)
BATT 3 & BATT 4 are both Motorcraft BAGM-48H6-760 (I believe these are 70Ah AGM batteries)

I'm not 100% sure what my needs are yet, but I think I'm looking to have around 300Ah of usable battery capacity.

OK, so that's the background information. Now for questions:

1. Can I use Lithium Batteries? I'm ok with dropping the existing AGM batteries if necessary, but I would ideally love to keep the ability to charge off the Alternator, and have the new batteries continue to power the existing circuits that I decide not to remove.
2. If I can use Lithium batteries, can I just drop-in-replace the existing AGM batteries in the circuit (maybe moving them inside to keep them at a more constant temp)? Do I need to do anything to protect the starter battery or alternator? Can I keep the AGM batteries alongside them for a little (70Ah usable) extra capacity?
3. If I can't use Lithium, from what I've read, getting 300Ah of usable battery capacity probably means having around 600Ah of AGM and 600W of solar. Do I have this right?
4. Either way, am I safe to just connect the solar charge controller to the left terminal of the master relay? Note that this means it will be a few feet of 2GA wire plus a few feet of 1/0 wire away from the batteries (See my schematic below) -- this is necessary because of where I would physically like to install the solar charge controller and the existing wire that's run. I can increase the gauge of the 2GA segment if necessary, but would prefer not to if avoidable.
5. If I add AGM batteries, I'll likely need to install some of them in a different location than the stock batteries. Do I have to worry about different lengths / gauges of wire meaning different voltage drops for different sections of the battery bank?
6. The system as it stands doesn't have a B2B or anything like that between the alternators and the battery bank. Is this something I need to change?

Here's a mockup diagram of what I'm hoping will be possible:


Thanks in advance for taking the time to read all of this. Hoping someone is able to help!