Lithium-ion (Li-ion) batteries power many of our everyday devices, from laptops and phones to power tools and electric vehicles. The 18650 cylindrical cell is a very common format for Li-ion batteries.
However, these batteries can become “dead” if discharged too low. The good news is that with the right tools and techniques, you can often revive 18650 cells and bring them back to life.
In this comprehensive guide, as a professional 18650 battery pack manufacturer, I will share how to safely revive and recondition 18650 Li-ion cells, step-by-step.
Why 18650 Batteries Die Prematurely
There are a few key things that can cause an 18650 Li-ion cell to die or lose capacity faster than expected:
Over-Discharging
Discharging a Li-ion cell below 2.5 volts can damage the battery. Repeated over-discharging cycles wear the cell out faster.
Storing in a Low State of Charge
Leaving Li-ion cells discharged for extended periods increases internal resistance and hurts capacity. Storing cells long-term at 40-50% charge is best.
High-Current Damage
Drawing too much current from a cell once can permanently damage it. Using the right load for an 18650 cell’s maximum discharge rating is key.
Old Age
Like all batteries, Li-ion cells lose capacity as they age. After hundreds of cycles, they may only hold 50-80% of original capacity.
Catching depleted cells before they die completely gives you the best chance of reviving them.
How to Revive 18650 Li-Ion Battery Step-By-Step
With patience and the right tools, you can often bring depleted 18650 cells back from the dead. Here is the process:
Step 1: Check Voltage
Use a multimeter to check battery voltage first.
Discharged cells will read:
- Full charge: 4.2V
- Nominal: 3.6-3.7V
- Discharged: 3.0V
- Overdischarged: <2.5V
If voltages are below 2.5V, the cells may be damaged but reviveable.
Zero voltage means the cell won’t hold a charge. Recycle cells reading 0V.
Step 2: Pre-Charge (If Needed)
If cells are under 2.5V, give them a brief pre-charge before full charging:
- Set power supply to 3.7V and 500mA current limit.
- Connect discharged cell and charge for 2-5 minutes.
- Check voltage again. Stop when voltage reaches 3.0V.
This small pre-charge brings the cell voltage up enough for normal charging.
Step 3: Full Charge & Analyze
Now use an advanced Li-ion battery charger/analyzer to charge and test cells.
Quality chargers like the SkyRC MC3000 can:
- Safely charge depleted cells
- Charge/discharge test capacity
- Measure internal resistance
Charge depleted cells at 0.5C or lower (slower is better). Then do capacity test cycles to check cell health.
Healthy 18650 cells should be:
- 2300+ mAh capacity
- <150-200 mΩ internal resistance
- <2%/month self-discharge
Step 4: Match Cells
Group cells with similar tested capacities and internal resistance for best performance.
Mismatched cells strain weaker ones when used in series. Poor performers hurt overall pack capacity.
Step 5: Assemble Pack
Connect matched cells in series/parallel to achieve desired voltage and capacity using nickel strips and an appropriate holder.
Soldering directly should be avoided. Welding is preferred for permanent low-resistance connections.
Use a protection BMS board suited to the cell count to prevent over-discharge and over-charge damage.
With TLC during charging and some testing equipment, depleted 18650 cells can be brought back to working order again in many cases. Match capacities well and use protections to prevent premature failure.
Safety First When Reviving Li-Ion Cells
Lithium-ion batteries contain a lot of energy and can be dangerous if not treated properly. Keep these safety guidelines in mind:
Charge in a Fireproof Location
Always charge Li-ion cells in a fireproof location. Use a LiPo safety bag. Have an ABC extinguisher on hand. Don’t leave charging cells unattended.
Avoid Short Circuits
Prevent shorting battery terminals together or to any other metal. Use insulating materials when handling bare cells.
Monitor Cell Temperatures
Stop charging if cells get hot, which indicates a problem. Dispose of any bulging or damaged cells immediately.
No Soldering Directly to Cells
The heat can damage li-ion cells and solder connections are prone to failure or resistance issues. Use welded nickel strips instead.
Slow Charging is Best
Charge at less than 1C current whenever possible, and at less than 0.5C for resuscitating depleted cells. This reduces stress and lengthens cell life.
With great care taken during handling and charging, salvaging “dead” 18650 cells can be done relatively safely. Always err on the side of caution.
It’s also smart to have a fire extinguisher nearby when attempting to revive lithium battery cells…just in case!
Frequently Asked Questions
Can I revive a fully dead 18650 battery?
It depends how “dead” it is. If a cell has been discharged to zero volts for a long time it usually can’t be saved. But cells drained down between 0.5-2.5V still have hope in many cases. The lower the voltage though, the less likely the cell can be fully restored.
How do I recondition old 18650 battery cells?
Doing full charge/discharge cycles with an analyzing charger can help rebuild capacity in lightly used cells that have lost performance over time. Check internal resistance too. But if cells tested badly or get hot, it’s best to retire and replace them.
What charger is best for reviving 18650 batteries?
Look for an advanced Li-ion battery charger/analyzer that has settings to revive over-discharged cells and can charge at less than 0.5C current. Quality brands are SkyRC, Opus, and LiitoKala. Avoid basic chargers without these cell analyzing features.
Can I revive 18650 cells in a laptop battery?
Yes, you can remove the cells from a dead laptop battery pack and try reviving them individually. Just be extremely careful when disassembling packs and separating out the cells from their protective circuit board.
How do I fix a 0V 18650 cell?
Unfortunately 18650 cells that have discharged all the way to 0V are usually too far gone to be fixed. A zero volt reading generally means an internal connection has been broken. These cells won’t hold a charge anymore and should be recycled.
Conclusion
Reviving seemingly “dead” 18650 lithium-ion cells is possible in many cases with some patience and the right revival tools. Just be sure to always make safety a top priority when attempting to recondition these batteries.
The key tools you’ll need are an advanced Li-ion battery charger/analyzer that can safely charge discharged cells and test capacity and resistance. Carefully pre-charge cells under 2.5V before fully charging and then analyze performance.
Group cells with similar tested specs to assemble longer-lasting and well-balanced battery packs. Always incorporate protection circuits too.
While not every depleted 18650 cell can be saved, this guide will help you safely revive all the good ones that still have life left in them.
