Expanding w/Unequal Capacity Batteries

[WearyWanderer]

My travel trailer (that I'm full-timing in) currently has two separate power systems:

• Two 12v 250Ah Chins self-heating bluetooth LFP packs (~40 cycles on them) paralleled in the front compartment along with a 100A PowerMax charger right next to it, all cabled to bus bars with 4ga copper cabling wired to the camper's main cabling
• A Bluetti AC200MAX with a B300 add-on battery in a side compartment (would be about a 15ft run from the front compartment), able to feed the entire camper AC and optionally power my DC circuits (all DC circuits are on DPDT switches so I can choose individually to run them off of the Chins or the Bluetti)

While having two power systems keeps a bit of redundancy in the mix, I'm considering ditching the Bluetti and adding in two more Chins packs in its place (along with an inverter) so I only have one system to manage.

I was hoping that with the low cycle count, I could drop in two more 250Ah packs and be on my way. Unfortunately, between when I bought the Chins packs and now, Chins seems to have discontinued the 250Ah bluetooth self-heating packs and instead now offers 280Ah packs in their place.

What sort of issues might I run into if I added two new 280Ah packs in parallel to the existing packs, assuming that I top-leveled them? Based on my thinking, the voltage from the 250Ahs should sag slightly, thus drawing from the 280Ahs more and keeping overall charge %s relatively equal. However, I've read enough people saying never to mismatch capacities, so I'm trying to get an idea of issues I might run into.

A second question would be how to cable two separate sets of bus bars together that are 15ft distant (two 280Ahs on one end, two 250Ahs on the other) but keep the draws/charging relatively equal. The 100A charger would be on the bus bars with the 250s, and the 2000w inverter would be on the bus bars with the 280s. I'm thinking one or even two sets of 2/0 copper cable connected between the bus bars would keep things relatively balanced, but I could be way off.

 

[12VoltInstalls]

This is not a scientific answer.
Nor is it technically a right answer.

Practical answer:
I would do your batteries mismatched like you suggested. ~10% difference
But the 15’ of run is more an issue. While it will probably work ok-ish I’d see if I couldn’t find a way to have everything within a few feet of each other.

 

[WearyWanderer]

This is not a scientific answer.
Nor is it technically a right answer.

Practical answer:
I would do your batteries mismatched like you suggested. ~10% difference
But the 15’ of run is more an issue. While it will probably work ok-ish I’d see if I couldn’t find a way to have everything within a few feet of each other.

Unfortunately, having them closer together just isn't possible. I really wish it was. Due to weight distribution with my travel trailer, I need to have this weight spread out in the two locations. The side compartment was great for the Bluetti, but it's the only place I'm going to have room to put the two new batteries (and inverter).

I'm HOPING that the one or even two (doubled-up) 2/0 cables between bus bars will create a connection with a low-enough resistance that it shouldn't be an issue. However, if it does prove to cause problems, the way I might be able to do it is have loops of cables to balance everything out (although that's a crappy messy way to do this).

 

[12VoltInstalls]

It may be usable as you described but not ideal.

Due to weight distribution with my travel trailer

~120lbs in a ?? 7500lb trailer seems like a small issue imho as it’s ~2% overall

Try it with the long cables.
It may have acceptable results.