Creating your own LiFePo4 12V battery is the cheapest way to get a brand new lithium battery for off-grid purposes. You can use them for your camper van/ RV. Or maybe you want to build a powerwall to store all your generated solar power. It is possible to use LiFePo4 as a starting battery for your car. But if you have a big engine, you probably also have a big start motor. Big start motors use a lot of electric power, so the battery has to provide all that power at once. Ensure that your batteries will provide enough current for your purposes since a starter motor can easily use 300A at once.
Pro’s & Con’s of a LiFePo4 Lithium Battery
|Extremely safe. There’s no flammable content inside the battery. There are endless videos on YouTube of people torturing LiFePo4 batteries like this one and nothing dangerous happens.||Can’t charge them under 0°C (freezing point) or you’ll permanently damage your cells|
|At least 90% of the rated ah can be used (50% with standard lead acid/agm batteries)||It can be a lot of money to purchase (but in the long run it probably saves you money)|
|Less weight per watt compared to a regular 12V battery||Not the best choice as starting battery for your car or motorcycle since you need to put more batteries in parallel to get enough ah at once. And when you live in a place where it is below freezing point (0°C) you can’t charge them.|
|Long lifecycle. After 2000 cycles you still have at least 80% of the rated ah capacity. (normal 12V batteries have 300-500 lifecycles if you treat them right)|
Choosing your Batteries
There are many different sizes of LiFePo4 cells, and it varies per project what you need. If space and or weight is not a problem, it’s probably safe to say that bigger (more ah) is better. Each cell is 3.2V, so to make a 12V battery we need to connect four cells in series (3,2Vx4=12,8V). When connecting batteries in series, the ah stays the same.
When you want more amps than you can buy cells, it’s best to make multiple 12V batteries and connect them in parallel. That way you can count the ah together. This counts for all the amperes, so you also increase the maximum discharge rate (count them together as well).
Our Battery Example
In this example, we have eight cells, and we’ll be building two 12V 200ah LiFePo4 lithium batteries that we will connect in parallel to get one 12V 400ah battery that I’ll be using for my camper van. When connecting batteries in parallel, you have to use the exact same batteries (same production date/number and used) because your system will be as good as the worst performing battery.
Why 400ah? I’m going to cook on induction plates because I’m tired of wondering how much propane gas I have in my tank. And I can also use the extra space I have without a gas tank. Further, electricity is available for free with solar panels, so I can cook on for a while. My inverter enables me to pull a peak power of 4000W, so I want a battery that can handle that as well. 4000W/12V = 333.33A, so four cells of 200ah with a maximum discharge rate of 200A won’t do. And having a little extra electricity is always nice for less sunny days. And at the time of ordering, they didn’t have the 280ah yet. Although 280 ah would not be enough, and 2×280=560ah would be a little overkill for my needs. Although more is always better if space and weight is not an issue.
This are 280ah cells that can deliver 280 amperes at once and can be charged at 140amps. Buss bars for connecting the cells in series are included.
Battery Management System (BMS)
When you build a battery with multiple batteries you’ll need to have a system that charges all the individual cells to the same voltage. While we’re at it we also want it to protect our batteries from overcharging and undercurrent, overheating, and undercooling. This is what the Battery Management System (BMS) is for. And we need it for the safety of the batteries, and also our safety. Unfortunately, bms’es with low temperature cut-off (that actually works) are hard to find. There seems to be a company in America that sells them but we don’t have personal experience with that BMS.
Common port BMS
There are different kinds of BMS’es with different ways of connecting them. Usually, the ones with a common port for the charging and discharging load can handle the most amps and are the ones you’ll want for your battery. The Symbol “B” stands for battery and this is where you connect the battery. “P” stands for load and this is where your charging/discharging will happen from. There’s also a “+” or a “-” sign to tell if it’s positive or negative. A wiring schedule with a common port usually looks like this:
Choose a BMS that can handle the specifications of your battery. In this example we build two batteries consisting of 4 cells ( we were gonna wire them parallel afterward remember). So we need two 4s LiFePo4 BMS that can handle 200A for our example. If a BMS is rated for more ah you can always use it for a battery pack that is smaller in amps. This BMS is the cheapest I could find and is available in all different sizes. Make sure you buy the one for 4 LiFePo4 cells, connecting through the same port
Making a 12V Lithium (LiFePo4) Battery
Although it’s not too difficult to build your own 12V LiFePo4 lithium battery, it is electricity and we’re dealing with big currents. So a word of caution is needed. If you have no idea what you’re actually doing, ask help from someone who worked with electricity before. That said, let’s get started:
Required tools (for the electric part)
When you’re like me and can’t strip a wire “like a real man” you’ll need a stripping plier like this to get those perfect stripped wires every damn time. Buy it here.
Crimping pliers to make an m6 terminal on your small BMS wires. Buy It here
The m6 terminals you’ll need for the small wires from the BMS. Buy them here
Serious wire terminals require serious crimping tools like this plier. Maybe you can borrow one or find a local shop that crimps the terminals on the wires for you if you don’t want to buy expensive tools like this one. Although it is possible to connect the terminals to the wire with a hammer for example. You want a good connection, and that can only be obtained with the right pliers.
Electrical tape can be useful to give the wiring some extra protection so that it never short circuits against other components. Buy it here
You’ll also need a piece of thick wire. Like 16mm2 or even better 25mm2 Get that locally. I used around one meter 16mm2 because I had it laying around. Also get some m6 nuts for the battery cells, and m8 bolts and nuts for the terminals in the lid.
Connect the cells in series
Since we need 12V we use four LiFePo4 cells that are 3,2V on average. We connect them in series with our buss bars. This means that we start from our negative, going to the positive of the same battery. Then connect this positive side with the negative side from the next cell. We repeat this until we are at the last positive side of our cell. That should give us approximately 12,8V. In this 200A example I used double buss bars to connect the batteries in series because I’d like to play it safe (more wire/material for current to flow through is better). Don’t bolt everything together just yet because there’s more work to come!
Connect the BMS
After the buss bars are connected, Let’s wrap them together. In this example, I used duck tape because… it’s duck tape. It fixes everything. Connect the small wires of the BMS to get an idea of how the situation would look like when it’s finished. Remember that there will be two thicker wires from the “B-” to the BMS, going to the “P-“. Check this image if the wiring confuses you.
Build a Battery Box
Since it’s rather unprofessional and unsafe to just leave everything wide open. And to make this battery more usable you’ll need a nice case for it. There are endless ways to build a box for it. This is how I did it with materials I had laying around. This box should be quite firm because the batteries are heavy (32kg)
Complete the battery
Protecting your battery from the freezing
LiFePo4 batteries have one big disadvantage: they can’t be charged when the temperature is below freezing (0°C). If you charge them when it’s freezing you will permanently damage the cells. Since they cost a lot of money that would be a waste. So in order to protect them from charging below 0°C there are a few things you can do.
Some expensive LiFePo4 battery brands use a small heating wire inside the battery case which starts heating when the batteries wil go below 0°C. I don’t like this because it uses electricity and I won’t be producing much when it’s freezing outside. You could make something with a heating element and temperature switch to get the temperature above 0°C when charging.
Another cheap idea I thought of is with this temperature switch. Since my batteries will be loaded from solar only we could set this switch so that the charge load disconnects whenever the battery gets below 0°C. I didn’t do this either because my solar charge current will be 40A max. The relay of this temperature switch can only handle 20A. So in order to make it work, I should use the temperature switch to trigger this bigger relay . That gives me a lot of useless power consumption just from the relays and temperature switch.
Since lithium batteries don’t like to be float-charged, your batteries probably won’t be constantly charged day in and out. So I choose the easiest solution: manually checking the outside temperature and disconnect my solar panels when it’s freezing using this circuit breaker.
It is possible to create a good quality LiFePo4 lithium battery at low cost. You’ll need to put some time and effort in but it saves you a lot of money. Work really precisely since you’re working with electricity. Make sure no wires will touch anything over time, even in a shaky environment like a car. Also, make sure that the connections are good and the wires used are thick enough. If you buy any of the items listed in this article, please order them through the links listed here. I made sure to look for the cheapest deal and get a small percentage of it which cost you nothing extra. When you feel unsafe ordering from aliexpress, read this guide: Is AliExpress reliable? A Beginners Guide.
Have fun building and using your homemade DIY LiFePo4 lithium battery!
Read our article “how to charge your LiFePo4 battery” to find out how to properly charge this battery!