How to Connect 18650 Batteries in Series
Connecting 18650 batteries in series is a great way to increase the voltage in your battery pack. By wiring batteries in series, you combine their individual voltages to produce a higher total voltage output.
For example, connecting two 3.7V 18650 lithium-ion batteries in series produces 7.4V. This stepped up voltage can power all kinds of electronics projects.
In this comprehensive guide, as a professional 18650 battery packs manufacturer, I’ll walk you through everything you need to know to safely connect 18650 batteries in series.
Why Connect 18650 Batteries in Series?
There are two main reasons you might want to hook up 18650s in series:
1. Increase Total Voltage
Like I mentioned earlier, connecting batteries in series sums their individual voltages.
So if you need to power a project that requires more voltage than a single lithium-ion cell can provide, wiring 18650s in series is the way to go.
For instance, most multi-cell vape mods run off two 18650 batteries in series to achieve 7-8V.
2. Retain Capacity
Wiring in series combines voltage while retaining capacity (mAh).
Four 2500mAh cells connected in series still provide 2500mAh, just stepped up to 14.8V.
This makes series arrangements perfect for building high-voltage battery packs with decent capacities.
Step-By-Step Guide: How to Connect 18650 Batteries in Series
Connecting 18650 battery cells in series is easy as long as you follow proper precautions.
Here’s a step-by-step walkthrough:
Things You’ll Need
- 18650 batteries
- Battery holder
- Hookup wire
- Wire stripper
- Soldering iron
- Solder
- Multimeter
- Hot glue gun
Make sure all your batteries match in terms of chemistry, capacity, and voltage. Mismatched cells can cause serious issues.
I highly recommend using a battery holder to securely hold each cell. These cheap plastic carriers prevent short circuits and make soldering way easier.
1. Insert Batteries Into Holders
Start by snapping each 18650 cell into its own battery holder, maintaining the same orientation across all holders.
The raised nipple on one end of the battery indicates positive. Make sure they all point the same direction.
2. Connect First Battery’s Positive Terminal
Take your first battery and lightly strip one end of a piece of hookup wire.
Twist the exposed strands together to prevent fraying. Then tin the end of the wire with a bit of solder.
This helps the wire adhere to surfaces during soldering.
Cut the wire to length if needed and solder it to the positive terminal of your first battery.
Make sure you heat the surface enough to melt the solder. Don’t apply heat too long or you risk damaging the innards of the cell.
3. Bridge Positive to Negative Terminals
Now grab your second battery in the series.
Strip and tin the other end of your hookup wire like before. Carefully solder it to the negative nickel strip on the top of your second cell.
This bridges power from the positive end of battery #1 to the negative terminal of battery #2.
4. Connect Remaining Batteries
To add more 18650s to your series string, simply bridge additional cells one by one.
Connect the negative strip of battery #2 to the positive nipple of battery #3.
Then solder the negative terminal of battery #3 to positive end of battery #4.
Keep leapfrogging your hookup wire to link each successive cell.
5. Terminate Final Battery
Once your last battery is soldered into the sequence, you need to terminate the open end.
I recommend terminating both the positive lead from battery #1 AND the negative terminal of your final battery.
That way, you can tap voltage from either end of the pack. Just make sure the two terminals never touch!
6. Test Voltage and Ensure Protection Circuitry
Before sealing up your battery pack, use a multimeter to verify overall voltage.
For example, four 18650 lithium-ions in series should give ~14.8V.
You’ll also want to implement over/undervoltage, short circuit, and thermal protection to prevent catastrophe if something goes wrong!
Once you validate proper voltage—and test protection measures—seal the assembly with hot glue or heat shrink wrap.
And that’s it! With proper care, your series 18650 battery pack will perform for years to come.
FAQs About Connecting 18650 Batteries in Series
Here are answers to some of the most common questions people have about hooking up lithium-ion batteries in series configurations:
Are There Any Downsides to Series Arrangements?
The main risk of series battery packs is cell imbalance.
If one battery drains faster than the others, it can drop below threshold voltage first. That cell ends up getting reverse charged—which can damage the innards.
Balancing circuits help mitigate this problem by shunting excess power around weaker cells.
How Many 18650 Batteries Can Be Connected in Series?
Hobbyists have built up some monster multi-cell packs, but things tend to work best in the 3-8 battery range.
Voltage climbs rapidly. So does the catastrophic failure risk if something shorts or overheats!
What Applications Use 18650s Wired in Series?
Vape mods, high-powered flashlights, and even electric bikes often use lithium-ion cells strung together in series.
These arrangements step up voltage while retaining sufficient current capabilities. Just be sure your device can handle the amperage!
What About Running 18650s in Parallel?
You sure can! Parallel arrangements maintain ~3.7V nominal voltage while multiplying capacity.
Just make sure you balance the cells and watch out for potentially massive current surges on shorts.
Do I Need Special BMS Boards or Wiring?
For small hobby packs, simple wire jumpers and hobby chargers/balancers work fine.
But larger professional setups —like electric bike batteries— absolutely require proper battery management systems to prevent catastrophe.
Conclusion
I hope this guide gave you a good overview of hooking up 18650 lithium-ion batteries in series configurations.
The basic process involves:
- Physically bridging positive to negative terminals cell-to-cell
- Making good solder connections
- Verifying overall voltage
- Incorporating protection circuits
Series arrangements step up voltage for higher power. Just be cautious, stick to tested electronics principles, and you’ll be in good shape!
And as always, reach out if you have any questions about safely connecting these versatile little cylindrical cells.
