18650 Lithium Ion Battery Capacity Tester




About: I am IT professional, living in Bangalore, India. As new gadgets come out everyday, we indulge in spending significant time and money on these gadgets. And our kids are learning from us, they know how to use...

Hi All,

I had bought few 9800 and few 4200 mAh lithium ion batteries from Aliexpress last year.

They were quite cheap... and as I researched more on them, I found that these are fake and their actual capacity may be very less.

Then I extracted Lithium ion batteries from old laptop battery. But wondered are these still at original capacity or have reduced their capacity

For a beginner DIYer it is difficult to buy expensive testers....

So, in this instructable, I will share how to make 1s lithium ion battery capacity tester

Please share your comments if you like this instructable.

Step 1: What Do We Need ?

- TP4056 with protection
- USB female
- USB doctor
- USB Load
- Battery holder
- Wires
- Wooden board

Lots of batteries from different sources

Step 2: Assembly

- Using hotglue, glue battery holder and TP4056 module
- Connect battery holder to TP4056 on +B and - B
- Connect USB to +Vout and - Vout

Check if everything is connected correctly

Step 3: Test 1 : GTF 9800 MAh

I had got 4 batteries for 6 dollars. It claimed to have 9800mAH

Claimed Capacity : 9800 mAh
Actual capacity : 1000 mAh

Just about 10% of what it claimed

Step 4: Test 2 : 4200 MAh

I had got 4 batteries for 3.5 dollars. It claimed to have 4200mAH

Claimed Capacity : 4200 mAh
Actual capacity : 500 to 600 mAh

Little above 10% of claimed capacity

Step 5: Test 3 : Laptop Batteries LG Make

I extracted these from old HP laptop battery

Claimed Capacity : 3000 mAh
Actual capacity : 2300 mAh

Not bad for 5 year old batteries

Step 6: Test 4 : Laptop Batteries Set Samsung Make

I extracted these from old HP laptop battery

Claimed Capacity : 2200 mAh
Actual capacity : 2000mAh

Not bad for 7 year old batteries

Please share your comments if you like this instructable.

2 People Made This Project!


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8 Discussions


5 months ago

Thank you for creating this - I thought of 2 questions (and related sub-questions) that I could not answer myself.

1. How long must you test each cell for an accurate capacity reading (mAh)? Or is the capacity reading accurate instantly as soon as you power up? (because the usb tester is performing the internal math / logic and providing output display?)
2. Your USB tester appears to have a timer (mine does not) - are those times in the pictures on the USB tester display in minutes or hours?

Thank you,

2 replies

Reply 3 months ago

A timer is not required if the meter displays the Ah or mAh. That is also a timer-indication: 1000 mAh = 1000 milliamperes for 1 hour.


Reply 5 months ago

Hi Dave,

I let the battery connected till completly discharged. The usb doctor i used shows total time the battery was able to support and during discharge the viltage and current varies, the usb doc is able to monitor and state total capacity.


11 months ago

The chip mentioned is also used on some phone battery packs.

I think its worth mentioning that some batteries work best if recharged before test, especially if they haven't been used for a long time (eg electric bike batteries)

For a single 18650 this is fine but larger packs may never charge due to thermal protection,

1 reply

Reply 5 months ago

Sorry i missed your message.
I will make a note of this


1 year ago

The range of the tester is 4V - 20V.

How you test the full battery capacity from 4,2V to 2,5V?

I test the tester and the voltages is very inaccurate under 4V.

The display under 4V becomes darker.

2 replies

Reply 1 year ago

Not for me, it is good tool 2.6v
my usb tester, is not rated for 20v, may be that's why, I am able to test lower voltage


Reply 1 year ago

Where you buy it?

My Keweisi tester has a range from 4V - 20V.

All Keweisi tester i found on www.aliexpress.com has a measurement range from DC 4-20V too.