I Made This Custom Battery Using 18650 Cells Because I Needed a Small 12v Battery For A Different Project And Everything Thing Else I Tried To Find Was To Expensive. I Wired 9 3.7v 18650 Battery Cells In A 3S3P Configuration Meaning I Have 3 Battery Cells In Parallel Then 3 Of Those In Series To Get 12v. The Batteries I Used Are 2,200mah Each So The Total mah Will Be 6,600. If You Have A Different Amount Of Batteries Or Any Questions Or Need Help You Can Join My Discord.

Supplies

9 18650 Battery Cells- The Website I Used To Buy These Batteries Is BatteryHookup.com. I Used These, The Only Problem Is They Are In A Different Casing So You Would Need To Take Them Apart Which Can Be Difficult.

BMS (Battery Management System)

Cell Spacers

XT60 Connector This Is Optional I Just Use This To Make It Easier To Charge And Connect To Things

18AWG Solid Core Wire You Could Also Use Stranded Wire But It Is Harder To Work With

Stranded Wire This Is Optional I Just Prefer It To Connect To The Input/Output Of The BMS And XT60 Connector

Spot Welder This Is To Connect The Batteries

Nickel Strips The Spot Welder Comes With Enough But If You Want More You Can Buy This

Multi Meter To Test Your Battery And Connections

Heat Gun To shrink heat shrink

Heat Shrink The correct size is Width 140mm and Diameter 89

Any soldering iron

A 12v Power Supply To Charge The Battery

Any Wire Cutter

It would be better to use a spot welder and nickel strips to connect the batteries but if you don't have one you can use a soldering iron. If You Are Going To Use A Soldering Iron Be Careful To Not Overheat The Batteries

Step 1: Put Batteries in Cell Spacers

Arrange 18 cell spacers in 2 3x3 patterns or as many as you need.

Now Put The Batteries In The Bottom Spacer Like The Picture Below With + Up In 1 Row Then - Up Then + Up Again

Once you put the batteries in the bottom spacer put the top spacer on. Make Sure You Do This Before Soldering Or Using A Spot Welder Or You Will Have To Redo It

Step 2: Wiring Batteries With Spot Welder

Using A Spot Welder Is A Lot Easier And The Best And Safest Way To Do This

If Your Using The Spot Welder That I Linked Make Sure The Spot Welder Is Set To Automatic Mode, Level 11, And Plugged In For Best Results

To start set the nickel strip on the first battery then hold the two prong next to each other until it spot welds it

After you spot weld the first time you should see two dimple as seen in the picture below

Now do that again on the same battery just below the first one so it holds better

After that line up the strip on the second battery and do it again for all three. Then cut the end of the nickel strip

Now do this for all sides of the rows top and bottom so it looks like the picture below

After you welder everything together flip it so the top has a positive row on the left and right with the negative in the middle and label or remember them as row 1,2, and 3 as seen in the picture below

After you have labeled them take more nickel strip and weld the positive of 1 to the negative of 2 as seen in the picture below

Now flip the pack over and weld the positive of 2 to the negative of 3

After you have done that take your multi meter and check to make sure you get around 10-12v if not you have wired it wrong

Step 3: Heat Shrink and Wiring Batteries to BMS

Now that you have wired your battery pack up it time to connect the BMS and heat shrink it.

What I like to do is heat shrink the battery pack then cut out holes in the heat shrink to wire the BMS and put another layer of heat shrink over the BMS

Heat shrink your first layer on as seen in the picture below

Take take something sharp and cut holes in the heat shrink on the solder points. You could also use a small torch or lighter to burn the heat shrink away

In the picture below you can see the parts I burnt away the part I burnt away are the main negative (Negative Of Row 3)

The main positive (Positive Of Row 1). The connection between + of 1 and - of 2. Then I burnt away the connection between + of 2 and - of 3

The reason I did it this way was so I could easily wire the BMS to it and make it look nice.

If this is to confusing you can just wire the BMS not in the heat shrink just make sure to connect B- to the negative of 3, B+ to the positive of 1, B1 to + of 1 and - of 2, and B2 to the + of 2 and - of 3.

Now we need to solder the BMS to the battery what I like to do is scratch up the nickel strip with the file that came with the spot welder to get the solder to stick better. It is also easier to connect the wires to the BMS before soldering it to the battery

I forgot to take a picture of the battery all wired up so im sorry for that

To test the BMS and make sure you wired it right take your multi meter and put the negative probe on the B- then take your positive probe and put it on the B+ you should get around 12v, then take the positive probe and put it on B2 it should read around 6-7v, next take the positive probe and put it on B1 you should get around 3v. If you get those voltages then it is wired correctly.

With this BMS to be able to get power out of the P+ and P- you first need to apply 12v to it after you do that you should be able to get power out of it and also charge it. With this BMS it will charge it up to 12.6v.

Now After you get the BMS wired up you can either leave it exposed or put another layer of heat shrink on. Take your next piece of heat shrink (I Like To Cut This Peiece A Little Bigger Then The First) and put it on the other way then use your heat gun to shrink that down and it is done. Below are pictures of it finished

Step 4: Wiring the XT60 Connector

To connect this battery to this and use it I like to add an XT60 connector to it to easily connect and disconnect it.

What I find easier to do is use 18/2 stranded wire instead of solid core wire so it is flexible. Sometimes stranded wire can be hard to work with so what is do is strip the wire twist it then put solder solder on it to keep it together. Then I will add some solder into the connecter. After that I will put some heat shrink on the wire just to give it some extra strength then put the gray piece on the the connectors come with (Make Sure You Do This Before Wiring It To The Connector). Then just solder the wire to the connector and your Done

If You Use An XT60 Connector You Can 3D Print A Cap For It With The File Below