1/2/B switch

[Half-Blind]

My house batteries are divided with a 1/2/B switch. House battery 1 is connected to 1 and battery 2 is connected to position 2. The start battery is separate. I want to upgrade to 4 lithium batteries. My question is can I just replace the 2 house batteries with new batteries and then wire a new battery in parallel to each side. I would then have a house bank of 2 batteries in parallel on position 1 and 2 batteries in parallel on position 2. If this isn't a good choice, can I just connect all 4 batteries in parallel to position 1 and just leave 2 empty? Thanks in advance.

[hjohnson]

In general, you do not want to use a 1/2/B switch with Lithium batteries. Due to their stupidly low internal resistance, you can wind up with very large currents if you hit the “Both” position with mismatched states of charge. Also, with a dedicated start battery there really isn’t a point to one of those switches anyhow.

When I went Lithium, I just went work one large house bank (460Ah at 12V) and then did a dedicated start battery. Keeps it simple. If I ever do lose either bank, I can put in a temporary jumper wire between my alternator and starter motor and bridge the two 12V rails that way. (Alternator is on the lithium system, starter on lead acid).

[Half-Blind]

Thanks for the response. My plan is just leave the switch on both all of the time. So, if I read you correct, having 2 banks of 2 batteries won't hurt anything, it just isn't the best way to do it. Is that right? This is just something I wanted to do until I can perform a more involved rewiring of my entire system in about 5 months. They way my system is just doesn't leave any space for updates. My alternator charges my start battery with a dc/dc charger going to the house bank.

[Statistical]

Technically yes you can do any of those but the question would be why have this switch at all. What purpose does it serve.

If it were me I would get rid of the switch (of just use it as a 1 bank on/off only) and build one large LFP bank.

Simple is good. Don't make things more complicated then they need to be unless you need that complexity to accomplish something.