Two banks, one Firefly, one lithium?

[foojin]

We have a 12v house bank of three 4v Firefly L16 batteries. We love them. With 200w of solar, they exceed our power needs. The only downfall is that if one of the 4v batteries fails the whole bank fails.

So I was thinking of adding a second bank as a backup. Then, because I am curious and would like to know more about them, I thought maybe a small lithium bank.

Financially it might not be a good idea, but is such a two-bank system possible? Would we need two separate charging systems?