OK you are forcing my hand. I have been reading about boat and RV LiFePO4 batteries for about 10 years. I decided to go with one 100 amp (semi usable) about 7 months ago. It worked well on the Cumberland and Tennessee River trips--but just for the two chest freezer/refers.
We cook with an induction burner in the heat of Florida. We also have a microwave, but no inverter at that time. That meant running the generator for cooking or microwave off the grid. (We have a back up propane cylinder single burner to use in the cockpit if necessary).
We added a second 100 amp LiFePO4 battery in Feb. I didn't get the install completely done before leaving for the Hontoon trip--didn't have the fans to cool the inverter installed.
We have: 2 Battle Born 100 amp hour batteries or a total of 200 amp hours (actually I will not draw them down to less than 10%--and 20% is more prudent)--so probably about 180 amp hours. Weight is 60#. To get this capacity with a lead acid or AGM batteries we would be in the 150 or up# weight, and over 3x the space. We have the 2 batteries under the bunk on the port side. There is a cut off switch and 200 amp fuse on both sides of the 00 cable running between the batteries and the inverter. This was switched. (Mistake #1 was using a Chinese copy of a battery switch--it melted after the second use--we just bypassed it.).
We have a Victron 12/2000/80 inverter charger. This has a remote panel, which reads on or off, and can change some of the perimeters of the inverter output. We had to re-do the "outlets" part of the 110 V circuit to feed thru the inverter. NOT the BATTERY CHARGER, WATER HEATER. No High resistive loads, such as a electric cabin heater. So we have a separate circuit for those. We also have two 12 volt circuits--one only for the two refer/freezers. The other is the start, and remainder of house, including the windlass.
The Victron inverter is a piece of magic--but it is large and fairly heavy. It puts out pure sine wave AC power--better than your mains power. If you have low voltage or over a certain amperage, the inverter will kick in and supply the extra power in synch with the mains or generator power. In other words, it would allow a Honda EU2200 to start an 15,000 BTU Air Conditioner , without an Easy Start. It also works as a interrupted power supply--if we loose AC to the boat--the plugs which are on the inverter circuit are switched to the inverter within several microseconds. The battery charger puts out 80 amps, profiled (programed) to be optimal for LIFePO4 batteries. There is also a small 12 volt charger for the engine start battery if you wish to use it. We have a separate 15 amp battery charger for the house batteries and start battery.
YOU CANNOT COMBINE THE LIFEPO4 BATTERIES WITH ANY LEAD ACID/AGM/GEL ETC. THE LI BATTERIES ARE A HIGHER VOLTAGE.
THE RESTING STATE IS ABOUT 13.2 TO 13.4 VOLTS, VS THE 12.6 TO 12.8 OF LEAD ACID. If you were to attach the two batteries there would be a massive rush of current from the Li to the lead acid--and would damage both!
Recently I found the solution to that: The Sterling battery to battery charger. It comes in 30 and 60 amps. Because I wanted to limit the charging to no more than 30 amps, and I only have 44 amps from the Honda 150, I went with the 30 amp model. Again, it has to be fused at the 12 volt start battery, and at the charger. There are two more fuses--30 amps at the beginning of 10 gauge run to the Li ion batteries, and at the Li ion batteries. The Sterling charger can also be profiled for the LiFePO4 battery--and is a bridge to the engine start battery which is the point of take off for the charge.
Sterling 1230 battery to battery charger.
I am monitoring this system with the Victron 700. I also have a BMS monitor for the house bank (and voltage of the start battery. The BMS is a larger monitor, but almost identical functions as the Victron 702. We also have Automatic charge relay between the engine start (A group 24 interstate FLA) and two group 27 FLA house bank batteries. When these batteries die, they will all be replaced with group 31 AGM batteries. There is manual method to use either of the house batteries, or both, house batteries for engine start.
This system is not cheap. The first battery was about $975. The second was $925. The Inverter charger was about $1155. The Sterling was $278. Wire and switches were about another $200. All total, well over $3,000. (I had to bribe Marie by promising her a new car....)
I also down sized my RV in the last 6 months. When I put house batteries in it, I went with AGM golf carts for several reasons, including the lack of a converter for the 200 amp alternator on the Diesel engine for charging the LiFePO4 battery. 6 months later, this has changed--and if doing it now, I might more strongly consider the Li ion batteries, because there is an isolator which will take the 200 amps for between the engine start AGM and the Li ion battery. It costs about the same as the Sterling battery to battery charger, but is not as sophisticated. and probably would not work well for an outboard motor.
I found the people at Battle Born to be quite knowledgable. There are many li batteries going into RV's and many cruising boats, as well as off the grid homes. Technology is rapidly changing and prices are starting to come down.
But there is a huge amount of power in these relatively small batteries--and all of the components have to be robust. I mentioned the issue with the battery switch--I now have a US made switch which handles the 200 amps fine. I also had an in line circuit breaker (40 amps) to the Sterling from the house battery. That is what was called for., It was Chinese, and kept tripping. So again, I will be changing this out for a Blue Seas unit probably 50 amps to be safe. The wiring, and terminals have to be very carefully made. I got a hydraulic swagger for the large terminals. We used a lot of adhesive shrink wrap.
The LiFePO4 battery cell voltage is about 3.4 to 3.7 per cell, thus one has only 4 cells per "12 volt battery". instead of the lead acid battery which is about 2.1 t0 2.2 volts and has 6 cells for a "12 volt battery". Also although the charging voltage for both AGM and LiFePO4 is about 14.4 volts, The profile of charging is much different--and perhaps out of the bounds of this post. Down the line we can go into this--but the Li ion battery can be charged much faster--and the terminal voltage, float voltage (not really recommended) is also higher.
Why LiFePO4 vs other li battery technology? It appears to be the safest. There are very few, if any reports of fire or over heating (if properly used). There is a battery management system in each case (size of group 27) which will shut the battery off, if over charged, or if being drawn down too low. Completely discharging one of these batteries will result in a $1,000 paper weight! Over charging can damage the battery. For our first single battery, I used the old West Marine portable charger with the AGM profile. It worked fine, but would not do the last 10%. So I bought a cheap (Chinese--this one worked) charger, specifically made for LiFePO4. It had a monitor built in--amps, volts, SOC. We used that to top things off. We used Anderson connectors for both the battery chargers or any use of high draw for the first battery, and left them in place in case I have to use that same charger in case of an issue with the Victron.
Although these batteries have a lot of energy--drawing at more than 100 amps can only be for a short time (for a 100 amp hour battery), so a single battery is not to be used as an outboard starting battery. Also we have a temperature probe hooked up to both the Sterling B to B charger and the Victron Inverter charger. If the battery begins to heat up, the chargers begin to back down the amount of current delivered.
More to follow as the discussion evolves.
Bottom line, we were very pleased with the LiFePO4 batteries and Victron system. We never discharged over 50%,, even going once two days without charging. We found that running the outboard about 4 hours a day pretty well brought the 200 amp hour system back up to over 95% SOC. We also found that the Victron 12/2000/80 brought the batteries up very quickly. Once we put the cube electric heater, Microwave, and induction heater on by accident--more than 30 amps, where I had the Victron set. The Victron picked up the extra amperage, for the couple of minutes it took me to realize that we had an over power situation. (The mains power was limited to 30 amps--and an additional about 5 amps was added in synchrony with the Mains power. No breakers blew etc. Not recommended, but a "test" anyway.
