New House Battery Bank

Fiddler’s house/inverter battery bank got so weak that I couldn’t brew a pot of coffee without triggering an inverter shutdown because of sustained low voltage. For the last several trips where anchoring was involved, I would start the generator in the morning to brew the coffee and recharge the batteries. The inverter also powers the PC that runs the navigation software. On the last trip while using the microwave underway, the drag on the batteries from the microwave and navigation equipment caused the inverter to shut down. So it was time to replace the batteries.

One of the primary killers of marine deep cycle batteries is failing to recharge them completely, which causes what is known as sulfation. Adding a bulk charge to bring the batteries up to 85% doesn’t take a long time. But the next absorption charge phase to fully recharge them to 100% takes a very long time to do using the generator and/or alternators. Consequently, they are routinely recharged up to only 85-90%, and this shortens their life. Although we got five years of significant use out of this battery bank, it could have lasted longer. Solar panels are a popular way to fully recharge the batteries without constant generator use, but I haven’t installed solar panels yet. Maybe someday.

Caterpillar in Peoria, IL, developed a new battery technology several years ago to address the problem of sulfation. These batteries are sold under the Firefly brand name. They use what they call microcell carbon foam inside the batteries that resists sulfation, allowing them to operate in a partial state of charge for long periods of time without a loss in capacity. That sounds perfect for boaters like me. They also are supposed to last 2-3 times as long as traditional batteries. So that is what I installed in Fiddler.

I removed 8 6-volt deep cycle batteries that were wired in series to make 4 12-volt batteries, that were then wired in parallel to make one 12-volt battery bank of 880 amp hours. To maximize the life of these batteries, they are to be discharged by no more than 50% before recharging. So theoretically I had 440 amp hours of use before needing to recharge. In reality, on a typical day/night I will use 200 amp hours. So the battery bank is really oversized for our needs. I don’t have many power hogs on the boat since I changed all of the lights to LED and the stove is gas. The refrigerator is the biggest power user. We also use use power outlets, TV, PC, etc. To use the air conditioning, furnace, or water maker, I have to run the generator. The pictures below show the old battery bank, newly painted battery shelf, Firefly batteries set in place, and cabling.

The new Firefly battery bank is 450 amp hours in size, almost half the size of the one being replaced. The Firefly batteries come in two sizes, a 12-volt 116 amp hour battery or a 4-volt 450 amp hour battery. I went with the 4-volt battery because they are supposed to last even longer than the 12-volt model in terms of discharge cycles, plus they take up less footprint space than 4 12-volt batteries with equivalent capacity. Firefly batteries are maintenance-free and do not need to be in a battery box as they are leak and spill proof. I purchased 3 of the 4-volt batteries and wired them in series for one 12-volt, 450 amp hour battery bank. Below are before and after pictures showing the old and new batteries.

If we continue to use approximately 200 amp hours per day/night, that amounts to about 45% of the Firefly battery bank capacity, with plenty of reserve because these batteries can be discharged by 80% without shortening their life.

Here is the finished installation with batteries secured and positive terminals covered. I am happy with the way the installation turned out.

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