Hello Robert!  Sri about the three weeks delay, but we've been busier than a one-armed rower here getting launched and doing the usual shakedown voyaging.

  We upgraded from AGM 4.5 years ago - we had a 2 X 8D AGM house with a Group31 Start battery on ATSA, our Tayana 48DS.  The AGMs were failing (after 9 years - we didn't owe them anything!) so I started the process of changing the boat over to LiFePO4.

  We went with 100% Victron - the 12V330amp battery with two 200amp "Smart BatteryProtect" switches and their "SmallBMS" - which isn't a BMS at all, just a terminal box, as the BMS controller is inside the Victron battery.  Victron uses external switching for their BMS' - the battery has the smarts - voltage and temperature sensors plus microcontroller - but does NOT do the switching internally.  The two 200a switches are fed signals from the SmallBMS to selectively turn off charge or discharge to/from the battery.  The system works - if the battery gets too hot or cold, or the voltage is too high it disconnects the charge side.  If the voltage gets too low, it disconnects the load.

  We retained the Gp31 AGM start battery.  It was already isolated and charged through a voltage-sensitive combiner, so we removed the combiner and installed a small (16a) DC-DC charger (Victron Orion _Tr_Smart) fed from the house load buss.  This keeps the start battery charged without overcharging.

  We already had a programmable alternator regulator (Balmar 612) a programmable AC charger (ProNautic 12-50) and programmable solar regulator (Victron 12/50) so we didn't have to make any changes there other than reprogramming.  Probably the biggest change was in rewiring the boat to separate the charge side (AC charger, alternator and solar) from the load side.  I also took the opportunity to clean up the battery and alternator wiring and install proper fusing (Class T on the battery).  I already had a spike protector (Balmar APM-12) so that was covered.

As an aside, we also have a Victron BMV702 battery monitor and a Victron Cerbo monitoring system, which means I can watch my electrical system from afar 🙂  You will want some sort of battery monitor to keep track of the State of Charge (SOC).  I had Link 10s before, but they won't talk to the Cerbo.

  Would I recommend this approach today?  I'm not sure - while the Victron approach does work, it isn't necessary for using the newer, less expensive alternatives in batteries, which contain their own internal BMS and switching.  It would work, however with any sort of external BMS setup, and the harware is easy & rugged.  Whatever the exact battery setup, you WILL need a programmable alternator regulator - preferably one that can either reduce the total charge current to something your alternator can produce full-time, or properly handle alternator temperature.  The Lithium battery will draw 100% of whatever your alternator supplies until it is about 98% charged - which will melt most unprotected alternators!  You will also need your other charge sources to be programmable to the requirements of Lithium.  

 For some excellent info on doing the Lithium changeover, check out:  marinehowto.com

 I am VERY satisfied with the Lithium system - I would NEVER consider going back to lead.  The ability to charge at max until its full, discharge guilt-free to 5% and enjoy higher discharge voltage until its almost flat

Let us know how it goes!

Hartley

S/V Atsa