How to make a 6s 4000mah Li-Ion battery pack

Recently I built a brand new 7-inch quad that I was going to use for long-range flying. I’ve read that Li-Ion batteries have higher energy density than LIPO batteries per gram. For the same weight you get more capacity mah.

In other words, that means longer flight times!

What are the cons?
The discharge rate are much lower with Li-Ion batteries than Lipo. That means you can’t do punch-outs or power loops in the park with them. However, cruising around should be just fine and that is what I intent to use these batteries for.

I didn’t find any good guides out there on how to make 6s battery packs, but they are surprisingly easy to make.

Voltage

Fully charged voltage
Lipo: 4.2v
Li-Ion: 4.2v

Nominal voltage
Lipo: 3.7v
Li-Ion: 3.6v

Time to land voltage
Lipo: 3.5v
Li-Ion: 2.5v

As you can see. Voltage values are almost the same with Lipo and Li-Ion batteries. The biggest difference is when you should stop flying. Li-Po batteries start to take damage when the cell voltage dips under 3.5v.

When you reach 3.2v the voltage will start to drop dramatically and you will most likely not be able to recharge your Li-po battery.

A Li-Ion battery can be discharged much more. At 2.5v it’s time to land, but if you want to play it safe you should land at around 2.6v per cell.

WARNING

Soldering on batteries can be very dangerous if you don’t know what you’re doing. If you are new to soldering I don’t recommend doing this. Holding the soldering iron too long on the battery poles can heat up the battery and BAD things will happen.

Now that we have gotten that out of the way. Lets start the guide. 😀

Shopping list

For this built you’ll need a few things.

Li-Ion Cells
For this build I used Samsung INR 21700-40T 4000mAh 30A li-ion cells. I don’t mess around with batteries so I bought them from a source I trust in Norway. I can trust 100% that these batteries are what they say.

Wires and plugs
You will need:

You will also need strong tape to tape the batteries together. I use gorilla tape or gaffer tape. You will also need electrical tape to tape the ends.

I used a last layer of electrical tape on the outside of the entire battery to give it a nice black finish. You can also use heat-shrink for this purpose.

Wiring diagram

As you can see in the diagram. You basically solder all the batteries together in one long line. Between each connection you solder a balance wire lead. It HAS to be done in the order as illustrated in the diagram.

I used battery solder sheets to solder the batteries together. I started with soldering connection 2, 4 and 6 together. See diagram under how I made a secure joint.

Then I added the balance lead wires. See the first wiring diagram. I flipped the batteries on top of each-other and used gorilla-tape to hold them in place.

Next step was to tape all three batteries together. Remember to add the negative lead and the balance wires in the middle of the battery for connection 3 and 7.

The hardest part of this built was to just make all the wires and leads fit perfectly regarding length.

A work in progress.

Solder up connection 3 and 5. Add the rest of the balance wire leads.

Wrap everything together with strong gorilla-tape or gaffer-tape. Hide the solder joints on each side of the battery with electrical tape.

Use electrical tape or head-shrink for last finish. Now it should look something like this:

6s 4000mah Li-Ion battery pack
6s 4000mah Li-Ion battery pack

Second Li-Ion build

The second battery I made in a 3×2 configuration. The long battery with a 3×3 configuration fits nicely under the drone, but on the top I needed something more compact. See picture below.

3×2 configuration

The method is identical with the first battery. It’s basically 6 batteries connected in series with a balance lead connected on each joint.

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