I did a full upgrade to lithium about a year ago and am now adding to my battery capacity which is currently 400AH with another 500AH in preparation for world cruising next year.
Lots of good advice given in the previous posts, and I would support much of what Scott has said about the challenge of designing a ‘system’ with lithium. Any idea of a ‘drop-in’ replacement lithium battery should be treated with caution for the reasons outlined previously.
if I can add anything to the debate it would be the use of a DC battery to battery charger (may have missed this?). I use a Sterling B2B 60amp charger between both my 90amp engine alternator and my 90amp prop shaft alternator and my lithium bank. This allows all my alternator charging into my lithium bank to be done via a programmed lithium profile provided on the B2B60.
As the alternators are both linked first to my engine starter battery (Optima red top), then through the B2B to my lithium bank, they cannot (easily) overcharge my lithium bank, preventing battery BMS from disconnecting due to high current. This system also prevents the alternators from being destroyed from a voltage spike due to BMS disconnect. As a fail safe I can also turn off the B2B manually to stop it sending charge to my lithium bank if I feel the need I.e. I don’t like floating my lithium batteries for long so if I am on motor for an extended period I simply switch the B2B off using the remote panel at my nav station.
This setup has worked well for me so far, so check it out if you are interested.