Given the long cycle life of LFP batteries, adding another one a year down the line is fine. Ideally it will be the same capacity and brand. The wide and flat LFP voltage/SOC curve means they won't fight each other like mismatched lead will.
Note that all batteries in parallel need balanced wiring. Your diagram shows a balanced config.
It's kind of interesting. My batteries are not all together, so they are not wired in a perfectly balanced way. My Lifeblues, over a year, with about three weeks total of boondocking and about 6 weeks with driving / hookups have between 30 and 33 cycles on them. They define cycles as a full discharge / charge cycle. So, they are balancing themselves pretty well, and will likely outlast the van based on the number of cycles. I think the Solar helps that, keeping the batteries from discharging as much and filling them up every day.
If it was mine and you had the space i would put in one 300ah life blue with the internal heater and take out the shunt and victron 712.
I would also consider the 12/2000 victron inverter.
On further thought 200AH life blue and run the moter when you have really high peak loads on you inverter.
Tom
I don't have any external shunt or monitor. The batteries themselves provide way more information individually. If one were going bad, you could tell. I got four 100Ah batteries because they fit where I already had space. If i were starting from scratch, I might have considered the bigger ones. It is nice that the 100Ah ones are not very heavy. All my batteries are in wells. It was a real pain to get the Lead Acid ones out and really worry about them slipping and shorting to the metal framing of the wells. You can pick up the Lithiums with one hand.
Regards,
Mark
