long review for Miboxer C4 smart charger [picture heavy]

I received a free sample of this charger from Miboxer to do this review on german Taschenlampenforum,
but also post it here on english.

They sent me in fact 2 chargers in the packaging for 2 chargers with DHL express.
So they did protect one retail box but the other got damaged due to DHL as there is no bubble wrap or other protection.
And its most likely the shipping is a lot more expensive than 2 chargers build costs.

The box contains:

- Charger

- 230V EU power cable

- AAA battery spacer for 2 slots

  • Manual

The UI is quite easy and good described in the manual so I don’t go further into it.
This review is long enough, for specifications look for them on their *website.

It charges all types of lithium batteries and NiCd/NiMh, the charger seems to double the NiMh current before the cell is full for a better termination.

The charger design seems similar to my Nitecore D4, my Klarus CH4S or clones.

It comes with a EU plug to my destination it has also a 12V port but no battery cable.

A really nice thing is the AAA holder so they make contact easily.
In my other charger I have to lift them to make contact properly.

Good charge characteristics for lithium and NiMh.
This is the first charger I have seen with higher peak charge current and measurement time decreased to get a better deltaV termination for NiMh cells.

The first thing was opening the charger to look inside, how well it is build.

The charger uses rails with sliders to make contact, all contacts and rails are made of coated steel,
copper would be nicer but being steel seems not to affect the voltage readings much.

The sliders may lead often to wrong voltage readings like my Klarus CH4S charger had due to bad construction of the rails even if it was made of copper,
as there might be a bad contact between the rails and slider and the steel having a too high resistance.

It also can affect the resistance measurement in slot 4 I get 60mOhms then I insert the same battery again and get different readings from 200-490mOhms, later more to the odd readings.

The resistance measurement with the directly soldered cell is always the same.

So first thing was to bypass the rails with 4 different wires to test this compared to the stock charger.

When disassembling the rails I saw some oil or other stuff on the rails and slider, not sure if it is to make better contact
or just oil for smooth sliding which may affect the resistance and give too high voltage readings while charging.

The manual is in English and Chinese,
but the fond is really small and extremely thin,
if it would be printed in bold letters it would be way easier to read.

The display comes with a protective film that is also labeled as such, often its hard to see if there is a protection film on the charger
so people don’t remove it.
The overall looking is better than my Klarus CH4S charger especially the shiny C4 looks good and the buttons fell comfortably soft.

The charger weights 285g so it is heavier than many other 4 slot chargers.

The charger has filtering after the power plug which is necessary for electromagnetic compatibility EMC.

On this side the high and low voltage parts are connected over the transformer and a safety capacitor the switching controller has a cooling fin.

The output from the low voltage power supply side to the charger board is filtered in a coil to get RF noise filtered.

The HV and LV sides is separated through a very large gap printed the MIBOXER logo on it really good for electrical safety.

The HV side looks clean.

The SMD parts got glued into position by a machine and soldered by hand on the power suply board.

The charger board is single sided the leads to the rails are thick and well soldered.

The springs are not soldered like in many charger so there is no risk that it gets loose.

The charger board is really clean the contacts are made of plated steel.

Both battery contacts have 2 raised points to make contact to 14500 and 18650 sized cells,
for smaller cells like AAA there is the adapter to raise the battery to those points, but they are not perfect.

The contacts need definitely other contact design for more contacr area to the battery.
Unfortinually it lead to problems making a good contact to my cells with a brass button as the contact surface is really small, so I modified the contacts.

The microcontroller.

On the right side of the board is a FET with heat sink for discharging slot 4.

There are nowhere openings for airflow on the side or back, the charger gets not too hot, but better cooling would be not bad.
Sideview of my Klarus Charger with openings for airflow.

The Nitecore Charger has the same design.

Display board looks good.

There is some oil on the sliders and rails not sure if this affects the electrical resistance positive or negative.

Slider has as well 2 raise contact points, this worked out not too good as the contact area is really small.

Soldered some different wires to see if it affects the voltage reading from stock charger,
the bypassed rails have always a very low resistance, even the small 0.25mm² wire has no significant drop with 0.01V at 800mA.

On the stock charger if its good contact i have same voltage readings as I can measure on the cell,
but putting in the battery again can be a difference up to 0.3V especially with my brass button cells.
On the right side with the 0.25mm² rail bypass wire the voltage reading is correct (all cells were discharged to same voltage and have about same capacity)
I think also that oil does no good between sliders and rails as well.



- high quality build

- good electrical safety and EMC

- can do a discharge capacity test

- easy UI

- can charge all common battery types

  • slowly ramping up charge current
    - the charger double charge current and decrease the time between voltage measurements for NiMh cells, when they are almost full, for a better termination,

  • this is really new and good*


- oil between rail and slider may result in wrong voltage reading when charging and wrong internal resistance measurement

- the contact points to the battery are too small especially the positive side, getting a high voltage drop when charging and discharging, leads to inconsistent measurements of the internal resistance

- no mAh count when charging only time, would be nice to see both

- too low current for AA and C type NiMh cells charger needs also 800mA here

  • the charger has almost no airflow cooling it as it has only on the back an opening for air but nothing on the side, but it doesnt get too hot on normal charging

Suggestions for the manufactor:

- mAh and time count for all slots when charging

- needs definitely other contact design for battery contacts

- NiMh large capacity recognation and switch to 800mA charge current

- please no oil on rail and slider

- rail bypass wire like in Nitecore chargers

- openings on side for more air flow cooling the charger

  • increasing the whole manual at least to DIN A4 format with larger and bold letters would reading be way more enjoyable.

Thanks for the review Lexel :+1:

Excellent, detailed review :+1:

HKJ also tested the charger


The minus of his tests is as well problems with battery contacts for IR measurement

And he discovered the charger doesnt terminate after charge which is bad for LSD NiMh and Lithium