A sudden cutoff of the built-in BMS of a lithium battery to prevent overcharging can blow the alternator diodes. For that reason it’s good to have a lead-acid battery attached to your alternator at all times, and the lithium battery bank can be bridged via a DC-DC converter or other method to balance charge current
That was the thinking 5-10 years ago.... Most 35 ft+ production boats come off the factory floor with the alternator tied to the house lithium bank. There's no point having a 180A alternator and a 30A DC-DC charger feeding a 600 Ah lithium bank...
Starter can use flooded, AGM or a properly spec'ed lifepo4. I was able to start my 3JH3E with my small Lifepo4 jumper pack, nothing else attached to the starter.
All my motorcycles and my outboard run on Lifepo4. So long as charging voltage is below 14.4V, it's compatible. Many older alternator regulators that charged AGM can also be used directly to charge Lifepo4, so long as the absorption time can be reduced to 20 minutes and the equalization is disabled. On a car, temperatures under the hood can be unvavorable for the life expectancy of a Lifepo4, so probably not a good fit.
I know many boaters that have accidentally gone to OFF instead of BOTH once the engine was started, their alternators were still ticking away years later. Is it good for the diodes ? No, I wouldn't do it every day. But a good quality alternator will handle a sudden disconnect at least a few times. The diodes are rated for 50V+ to help protect the circuit from transient spikes.
The balmar APM is nice, as it has a monitoring LED, but you could just as easily use a TVS diode and check it once a year when you do an oil change.
Things are changing quickly in the electrical world and new boats are very complex. I suspect new boaters will have a very difficult time figuring out the root cause when something doesn't work, without dealer/factory support. My boat isn't super complex, yet I still need to refer to the wiring diagram and installation notes when working on something I installed a few year back. Just documenting the programming for all the charging sources (7), Cerbo GX, NMEA2000-wifi interfaces, etc.... took over a day.
Is the complexity worth it ? Absolutely. I remember having to run the engine for 1-2 hrs twice a day to keep the fridge going and using an oil lamp to save power. Now we don't think about power and never run the engine to charge. I can go for a week without solar or the engine. The system knows when the battery is nearly full and will dump the extra solar power into the 120V AC hot water tank. The system knows when to drop the charging amps and will coordinate the alternator, MPPT and inverter/charger in case they are all trying to do the same thing. If there ever was a warning or fault with the house bank, I'll get a message at the helm long before the BMS goes into shutdown. This is a simple system compared to a modern 40-50 ft cruising boat that may have 240/120V AC, 48V and 12V DC, but I've taken it as far as I can for this size of vessel.
I see solid state batteries (meaning solid electrolyte) are already in production and in use in some cars and motorcycles. Nigel C. will have to update his book every 1-2 years the way things are going.
Lifepo4 works. It's SUPER safe. Like anything else in life or boating, it has to be spec'ed for the job.
