Test/review of The minimum charger

The minimum charger

This is a combined charger and power bank in the minimum possible size.

It arrived in a cardboard box.

The box contained the charger, two usb cables and a instruction sheet.

Power input is a micro usb socket on the side of the charger.

There is a indicator led hidden behind a hole, in will flash a number of times depending on the battery voltage.

At the minus side is a micro usb shaped hole, it is for storage, there is no connection inside it.

Here the hole is used to place the charger in storage position.

The minus side is flat and the plus side has a hole in the connection, this makes it possible to use button top cells.

It is possible to plug the charger (Power bank) directly into a phone.

But it is better to use the supplied extension cable, then there is less stress on the connectors. The charge current may be slightly lower due to cable resistance.

The charger is designed for 18650 batteries.


  • Power consumption from usb when idle with no batteries is about 1mA

  • Will discharge a battery with about 0.3mA when not powered

  • Below 2.9V the charger will charge with 400mA to 250mA

  • Above 2.9V the charger will use full current.

  • Will restart charging if voltage drops below 4.05V.

  • Will restart charging if battery is inserted or power cycled.


A nice CC/CV charge curve with about 200mA termination current.

This is a good charge.

For this worn battery the termination current is a bit high and the voltage drops significantly when charging is terminated.

This battery is even older and the charger started by draining the battery a bit, because it went into power bank mode. When the current was turned on the charger very fast got the battery up in voltage and turned into constant current mode. The charging is fine enough.

A 0.5ohm resistor in series with the usb power to simulate a long cable or weak supply will reduce the charger rate significantly.

M1: 35.3°C, HS1: 54.2°C

M1: 46.5°C, HS1: 57.2°C

Being a fairly simple charger I could draw the current profile.

The charger is need a few seconds to start.

Power bank
  • Will discharge a battery with about 0.3mA when not powered

  • Will discharge with less than 0.02mA below 2.8V

  • Usb output is auto code with Apple 2.4A, Samsung and DCP

  • Cannot be used as UPS, there is a short power break when input voltage is removed.

The charger can deliver about 1.9A with a full battery before output drops.

When powered from usb it will pass the current straight through.

Also with a battery in the charger it will pass the current straight through when powered from usb.

The voltage starts dropping shortly before the battery is empty, the actual termination is not very good, it will reconnect every time the voltage increases.

At 1A the voltage drops a bit earlier and the reconnect is much worse.

At 0.5A the noise is 23mV rms and 101mVpp

At 1A the noise is 36mV rms and 236mVpp

Power consumption from LiIon battery when idle.


This is a small charger, that is limited to battery with 18mm diameter and can handle 1.8A charge current, i.e. 18650 batteries. In addition to the charger one or two loose cables are also needed. The charging works fine for good batteries.
It also works fine as a power bank, but the coding is a bit optimistic compare to its abilities. The noise is low. The charger do not handle it well when the battery is running low (The battery will not be damaged).

I will rate it as good for charger, and fairly good for power bank functionality.


Here is an explanation on how I did the above charge curves: How do I test a charger
How do i test usb charger and power banks

Could be a handy wee travel powerbank/ charger :+1:

I really like it as a unit to drop into my laptop pack. But, I can’t find where to get one of these… any idea?

Xanes XC01

I think this is it. Looks like it has a Type C, Micro USB and Iphone version

I am looking for a minimalist 18650 charger/powerbank that I can also use to check battery voltage so I saw this. Does it blink battery voltage like Anduril or Nitecore F chargers (2 sets for Ones and tenths respectively)?


A multimeter is your friend, aswang.

Thanks for the quick response hjk. In most cases, I always have a mutlimeter ready but in special cases like caving they’re not practical, especially with the lead wires. I guess the nitecore f1 will do for the moment.

aswang if you are willing to modify your devices and have skill to do so, maybe you could stick a small voltmeter with a pushbutton inside some of your caving lights:

https://www.fasttech.com/products/1005/10017168/3682003 3-pack yellow.

https://www.fasttech.com/products/1005/10017168/3682001 3-pack green.

Other colour models and quantities available, use the drop down to the right.

The above voltmeters have good accuracy and can be calibrated via a tiny potentiometer at the back. I myself bought a 3-pack of green units and compared plus calibrated their measurements versus my multimeter. They work with just 2.4 V and a smidge lower as specified, though at that point they are quite dim. I'd also say they're 3-wire but only come with 2 by default. Small and lightweight, they drain ≈10 mA if I do recall right. Recommended.

Where would you attach a third wire?
I assume that’s to connect an external battery, so it doesn’t drain the cell being tested?
So you’d add a white wire somewhere, and, um ….?


To better illustrate my point, let's take a look at a different but very similar voltmeter:

https://www.fasttech.com/products/1005/10017168/3866800 Single 0 - 100 V range voltmeter with blue led display.

As can be seen, the third or signal line (yellow) is right next to the power line (red), being the black wire common negative or common ground.

Uh! Mmm, the jumper next to the calibration potentiometer should also be removed, I think.