Of course if you had good lithium batteries all this charging stuff would be much simpler...;-)
However they are spendy.
Li-Ion batteries require some very fussy voltage charge profiles during both charging and discharging, that includes nasty and simple stuff:
voltage, current, temperature, voltage limits, charge balancing between cells
100X more complex than lead acid, the charging systems associated with larger Li-Ion battery packs involve multiple voltage sense, current sense, temperature sense and micro-controller systems to get the charging right and balance it across multiple cells, which becomes more of a headache as the batteries wear down.
One guess how I earn my living...
Actually the LiFePO4 bank on our boat has been quite simple. When you are charging and discharging at fractional "C" levels it is really not all that complicated.
..I do have a BMS but use it as a fail safe as we charge to voltages below where any cell balancing would take place. As of today we have 164 cycles on the bank most of them to 80% DOD. We physically turn off charge sources and purposely cycle to 80% DOD. Because these batteries don't need to get back to 100% to be happy I can leave them at what ever SOC I want when I leave the boat. They do not change temp when charging or discharging, measured it numerous times and early on had two temp sensors with digital displays mounted directly to them. In 164 deep cycles (more than many boaters even get out of LA batts) the cells have not budged one iota in balance.
I have it set right now to charge at 0.3 C via alternator and it charges beautifully and fast all the way to 98% SOC before it even begins to limit current. Cell voltages still agree out to the hundredths of a volt at 100% SOC and at 80% DOD... Setting up the Balmar MC-614 was the biggest challenge because I wanted the alt dialed to a point where it could run all day long at 120A, and this meant playing with the field settings to get it just right. I actually wound up at about 110A and that worked and kept the alt out of temp limiting..
I was considering going to a hairpin wound alt in the 200A range, setting it for 160A, but she charges so fast as it is that we often run the engine without the alternator even on.....
The real benefits for us have bee:
No voltage sag
80% of the capacity is actually usable vs. 30-35% with LA
Charges as fast as you can dish it out all the way back to 100%
The fridge actually runs less because the compressor works better at 13.2V rather than 12.2V
Not impacted by large inverter loads and voltage barely sags, even with 100A plus loads.
Separate loads bus and charge bus
Low voltage cut contactor for low voltage protection
High voltage cut relays for alternator and solar for high voltage protection
I will top balance each winter and as of this point they don't even need it.. The technology is simply amazing.. Our on-board equipment such as 12V refrigeration and Espar heat have never been happier, they have never run so well.. Voltage rarely if ever drops below 13.2V...
Oh and I built it for about the same price as buying four Odyssey PC2150 group 310 AGM's...
A build like this is well above most DIY's but the technology will catch up...
400Ah LiFePO4 Compass Marine Battery & BMS Module