The battery project
Replacing the house batteries (those that power the lights,
electronics, pumps, fans, refrigeration, etc.) was a huge project taking
me two years to plan and install. I replaced three 8D size AGM deep
cycle batteries, weighing 468 pounds, with this one LFP battery that
weighs one third less and fits in the same space as one of the AGMs. If
I take care of it, it will also outlast the AGMs many times over. They
are easier to charge and much more efficient. They are also much more
expensive and a bit bleeding edge in the stodgy world of boats. They
are so different that the tried and tested rules and systems (which many
boaters don't understand anyway) do not apply.
The way they are charged is critical since they are so efficient that they can cause alternators to burn up unless they are programmed to slow down. They also do not like being overcharged so you can't just leave a dockside battery charger or solar chargers on in an uncontrolled way as it will destroy the battery. The old tech is more forgiving and boat systems, in general, have developed around this forgiveness, and owners have become used to the older tech and don't pay enough attention to the batteries. Even old tech batteries can be ruined, and often are especially by cruisers, by inattention and improper charging and discharging. The LFP batteries is even more sensitive to being overcharged and over discharged so the battery management is more critical, especially given how expensive they are.
Fortunately, I was a marine electrician once upon a time and there is lots of advice and proven systems on the water from those before me. The online forum, CruisersForum.com, has been essential in providing information on best, and worst, practices, although there is still some significant disagreements on specific how to's and musts and shoulds. There is also some downright wrong "information" as you see on any public online forums these days. I think I have designed and implemented best practices from all of it and am already very happy with the battery. I had them sitting on my garage workbench for two years and they did not lose any charge - none. Amazing. They charge super fast and I can't leave my solar power on, nor do I need to.
The usable capacity range of the LFP battery is also dramatically better, throwing out the old rule of thumb of never letting your battery go below 50% of charge. So with old tech you can only use half (actually less than half the rated capacity) the capacity of an AGM battery but you can use 80% of the rated capacity of an LFP battery. So 80% of 400Ah (amp-hours - a measure of deep cycle battery capacity) is 320Ah. For an AGM, 45% of three 170Ah batteries is about 230Ah. So for one third the weight and one third the size you get 1.4x the usable power storage. And this is without any significant reduction in the voltage in the usable range so a motor will turn over just as strong at 20% as it would at 80%. Not so with old tech, like when you run down your car start battery and it is harder and harder to start your motor.
The way they are charged is critical since they are so efficient that they can cause alternators to burn up unless they are programmed to slow down. They also do not like being overcharged so you can't just leave a dockside battery charger or solar chargers on in an uncontrolled way as it will destroy the battery. The old tech is more forgiving and boat systems, in general, have developed around this forgiveness, and owners have become used to the older tech and don't pay enough attention to the batteries. Even old tech batteries can be ruined, and often are especially by cruisers, by inattention and improper charging and discharging. The LFP batteries is even more sensitive to being overcharged and over discharged so the battery management is more critical, especially given how expensive they are.
Fortunately, I was a marine electrician once upon a time and there is lots of advice and proven systems on the water from those before me. The online forum, CruisersForum.com, has been essential in providing information on best, and worst, practices, although there is still some significant disagreements on specific how to's and musts and shoulds. There is also some downright wrong "information" as you see on any public online forums these days. I think I have designed and implemented best practices from all of it and am already very happy with the battery. I had them sitting on my garage workbench for two years and they did not lose any charge - none. Amazing. They charge super fast and I can't leave my solar power on, nor do I need to.
The usable capacity range of the LFP battery is also dramatically better, throwing out the old rule of thumb of never letting your battery go below 50% of charge. So with old tech you can only use half (actually less than half the rated capacity) the capacity of an AGM battery but you can use 80% of the rated capacity of an LFP battery. So 80% of 400Ah (amp-hours - a measure of deep cycle battery capacity) is 320Ah. For an AGM, 45% of three 170Ah batteries is about 230Ah. So for one third the weight and one third the size you get 1.4x the usable power storage. And this is without any significant reduction in the voltage in the usable range so a motor will turn over just as strong at 20% as it would at 80%. Not so with old tech, like when you run down your car start battery and it is harder and harder to start your motor.
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