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#501 Single-cell Lithium Charger

How to charge a single 18650 lithium-ion cell with a TP4056-based charging kit, with comparison to ETA9635/ETA9638-based modules.



Lithium Ion/Polymer batteries are all around us these days, but they are also have a deserved reputation for being a bit dangerous if not treated properly, in particular:

  • over-current/short-circuit output (same situation can be created if the package is punctured)
  • over-discharge - increases battery resistance and hence heat/fire risk during recharge
  • over-charge - stresses the battery and compromises safety

Get anything wrong, and there’s heat & fire risk, maybe violent enough to be explosive. Great news for youtubers like Big Clive!

Charging is where things can most commonly go wrong. A little bit of knowledge can go a long way, especially if buying “cheap” chargers or going the DIY route.

There is an optimal charging profile for li-ion batteries:

  • pre-qualification stage - a low constant-current charge to bring deeply-discharged cells back to a nominal voltage (usually 3V for 3.7V li-ion)
  • constant-current fast chage - usually 0.5C until battery approaches fully charged voltage
  • constant voltage saturation charge - until charge current falls below 3-5% percent of the rated current.

This sensitivity to charging conditions is why li-ion cells are ideally charged individually, or with a balanced charging circuit when multiple cells are in an array.


  • Charging rates are specified in terms of C, where 1 C equals the maximum current the battery can supply for one hour.
  • li-ion with the traditional cathode materials of cobalt, nickel, manganese and aluminum typically charge to 4.20V/cell. The tolerance is +/–50mV/cell.
  • some nickel-based varieties charge to 4.10V/cell;
  • high capacity Li-ion may go to 4.30V/cell and higher.

Some guides to lithium battery charging:



The TP4056 is made by NanJing Top Power ASIC Corp. It is a complete constant-current/constant-voltage linear charger for single cell lithium-ion batteries, described as: 1A Standalone Linear Li-lon Battery Charger with Thermal Regulation.

The charging charge profile is designed for 3.7V li-ion batteries, featuring:

  • constant-current/constant-voltage
  • Preset 4.2V Charge Voltage with 1.5% Accuracy
  • C/10 Charge Termination
  • 2.9V Trickle Charge Threshold
  • Thermal Regulation


Typicall application circuit:


Julian Ilett did a very good detailed review and test of the common TP4056 modules:


TP4056 Charger Kit

I picked up an 18650 charging & power pack kit from an aliexpress seller: DIY Kit Micro USB 5V 1A 18650 TP4056 Lithium Battery Charger Module +600MA SB Mobile Power Boost Board +18650 Battery Box Case. It basically includes a battery holder and two modules: a TP4056 charging module, and a boost converter for a 5V output.


The TP4056 charging module uses three main chips in addition to support passives and indicator LEDs:


The boost module is a standard switching circuit using a switching regulator marked E50D. Although some listings identify this as a CE8301 regulator, the package marking don’t seem quite correct (appears more like a SOT-89-3 CE8301A which I would expect to be marked “A50P”). Regardless, this is the simplest form of fixed output converter without frills such as auto-shutdown.

Rprog/R3 is populated as 1.2kΩ, which corresponds to programmed charge current of 1000mA.


The recommended configuration matching the parts in the kit is a simple wiring together of the modules:


However, since neither the charge or boost module include any auto-shutdown capability, this means an “always on” configuration. I added a switch to the battery leads so that I can leave a battery in the holder without it being continually discharged.



Full charged:


TZT Single-cell Power Bank

As a comparison for the TP4056-based circuits, I opened up a TZT 18650 USB Power Bank I had kicking around.



It turns out this is using the ETA9635 which is an integrated charger and boost converter from ETA solutions. NB: The ETA9635 appears to have been superseded by the ETA9638.

This obviously allows for a much more compact product:


The ETA9635 features:

  • 2 in 1: integrated synchronous boost plus charger without external load switching
  • Short-circuit Protection
  • Reverse current Protection
  • Up to 1A Charging, 5W output
  • 50µA of quiescent current during no load

Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.