I am sold on Lithium Iron Phosphate batteries. These are also known as LiFePO4 or just LFP batteries. The difference between them and Lithium Ion (Li) batteries is that they don’t have a tendency to burn like the Li batteries in your phone, laptop or Tesla. BUT, not all LFP batteries are equal.
I buy all kinds of stuff, just to try it out, so I have accumulated a number of variations. My boat has two homemade units, each consisting of 8 320 amp-hour (ah) cells and a Battery Mangement System (BMS) board. The house has five store-bought LFP storage cabinet units of 314 ah capacity at 51.2 volts. As of this week, both of my electric farm trucklets have 51.2 100ah LFP batteries.
The two giant lead batteries that are also on my house system are 10 years old and still running strong, but when they die, they will be replaced with more LFP. I’m tired of water and acid and corrosion and long generator runs to equalize and desulphate them. There’s none of that with LFP! Best of all, LFP is now cheaper than lead batteries and lasts much longer, making them a better deal.
Let’s look at the DIY batteries in the solar boat, Sun King. A friend did a direct import of a big pile of cells and talked me into taking a few at wholesale price. He and I both are of Scots descent, so I’m ok with wholesale. Two groups of 4 cells are clamped together and placed in the sort of plastic battery boxes you see in boats. They are connected in series to make around 25 volts. The BMS board is in series and controls power coming in and out to keep the delicate cells from getting damaged by over- or undercharging. In this case, I also have wireless access to all the internal information via a phone app and I have a little display at the helm, serving as a “gas gauge.” ONE of these batteries has roughly 3 times the capacity of the lead batteries they replaced. These DID cost more than new lead batteries at the time, but I should not have to replace them every 2 years, so there is that. The price of the lithium mineral has come down dramatically in the last couple of years. They’ve found it isn’t so rare after all and new mines are coming on line. Battery prices have plummeted.
The batteries aboard Sun King have evolved over time. The original BMS, whose maker I do not recall, had a built-in balancer to keep the cells all at the same voltage, but it only balanced when charging at the higher levels of charge. Well, one of the features I like about LFP is that you don’t have to keep it fully charged to keep it healthy. Lead batteries have to keep topped up. The problem with that BMS was that in the partially charged state, cells could get out of balance at a lower state of charge. One of the jobs of the BMS is to not only protect the whole battery, but the individual cells, too. So, I was returning from Pensacola late one night, traveling through probably the most perilous part of my route and, suddenly, the power goes out! It is pitch black, the motor stops running and I am drifting backwards to my doom! My phone was lit up with a navigation app, so I was able to find it, call up the wireless app to talk to the battery and program access to a little bottom end reserve I like to keep. I was barely able to make it to port, and had no desire to repeat that performance.
That is something to remember about LFP batteries. They don’t just kind of peter out, they just quit when the BMS says they are done! When I analyzed the data, I should have had enough power to run until daylight, but ONE weak cell in each battery shut me down. I quickly found that a JK BMS with ACTIVE balancing would solve my problem and it did. Remember the part about active balancing.
Now to the house batteries. Internally, these are pretty much the same as my boat batteries, except wired in series for 51.2 volts and put in a pretty cabinet that looks fine behind the sofa in the Man Cave.
Like the boat batteries, these use the same JK BMS, wireless app and they have a display to keep up with state of charge. An advantage of having full access to the internals of the battery via the app is that you can program a narrower range of use for longer life, or keep a little reserve power or keep ahead of possible problems. I have identified one cell in each of Units 1 and 2 that requires a little extra attention from the balancer circuit. Could this be a future problem? If one becomes a real problem, I know which cell to replace. Meanwhile, I am loving the extra capacity. I think it got down to 40 degrees here last night and I ran the heat pump instead of the wood furnace. No problem. No trip to the wood pile.
This is what the insides of a Lithium Iron Phosphate battery system cabinet looks like. This is where the magic happens.
Let’s move on to the buggies. I bought a really impressive battery for my main hauler. It is in a waterproof metal case, has a display that can be remote mounted on the dash and I can look inside with a bluetooth app. Or maybe it is WiFi. Anyway, the phone talks to it, but not with the same app JK uses. I was disappointed find that I cannot change the programming, but at least I know the state of charge (SOC) and I can monitor the voltage of each cell. Remember what I said about how LFP batteries just quit when they are ready? Individual cell voltage tells me a lot about battery health and it looks like the BMS probably has active balancing. Installation was simply a matter of pulling out the old lead batteries, cleaning up the corrosion mess and placing a plywood pad on the angle iron battery rack. This battery is rated about half the amp-hours of the lead batteries, but LFP batteries have a higher useful capacity. They also have a lower internal resistance, which means they can crank out some amps. Early attempts to put LFP into golf cars ran into some BMS problems. My buggy has a 600amp motor controller and draws about 100 amps going up a hill. Yes, we have hills in Florida. Early batteries did not have the surge capacity. This BMS is rated for 200 ah continuous and peaks at 600 amps for a moment. The result is I have a battery that has greater range and should outlast me. On the downside, I can’t just pile things on haphazardly and stomp the pedal. This thing scoots and will not hesitate to dump a load upon acceleration. You can put up to 4 of these in parallel and I think they would be great for a boat, cabin or backup power system.
Installed and ready to run. There was plenty of room left, so I put a charger in there, too. On the downside, I don’t know who made the BMS or if it has active balancing. I like the handles for lowering that 90 lb. beast into the hole.
The other buggy got a really low-end battery I kinda bought by accident. I hate online banking, because it was only hours before my wife discovered the $600 missing on the credit card. Still, I had a buggy that struggled to get out of the shed and now I have a useful machine. This battery is in a standard plastic case. There is no communication with the BMS. No SOC power gauge. I don’t know if it is really 100ah (but will run a test). I don’t know if it has active balancing. I DO know it cost less than half a set of lead GC2 batteries. It weighs less than one of the original NEV batteries. It takes up about 1/3 of the space of a GC2 set. If it is what it says it is it should last longer that I will, but that’s not saying much.
A no frills 51.2v battery. Note the open area left of the battery. An inverter goes there for mobile power. An insulated wrench is a good idea for battery work. If you don’t have one, the auto parts store should have some dipping sauce to coat your own tools.
The battery layout on this machine has a divided plastic tray in the main area and the battery dropped right in. The other half of the tray got a 48v to 120v inverter that has previously been in the back. This buggy has a very low deck and is great for carrying a table saw, welder or other handy things and the inverter runs anything that needs to be powered.
Maybe I should not worry about not having communication with the battery. I did not have it with the old lead batteries, after all! One thing that some folks have encountered with cheap Chinese batteries is fakery. A battery will arrive and a meter shows it to have the proper voltage, but it just won’t perform. Prying the top off, they then find it is assembled with used wire, no BMS and small, second-hand cells pulled from street lights. The rest of the case is filled with sand. There are many brands you’ve never heard of and a few are working hard to become household names. Some just want a quick buck. So far, I’ve had pretty good luck, but what if one of those cells goes bad in the cabinet behind my sofa? You think I’ll ship that 300 pounds back to China in hopes they will replace it under warranty?
There ARE some household names in batteries. The old line lead-acid makers and vendors have seen the handwriting on the wall and have come out with their own lines. Trusted names like Trojan and Rolls have some pretty impressive product lines and some newer companies, like Fortress, offer quality products. They cost more than something you’ll find on Alibaba, but you can trust what you are getting and there is USA support, maybe even local support. You get what you pay for.–Neal