Charger Efest BIO
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Efest is selling LiIon batteries and liIon chargers, in this review I test one of their chargers. This model exist both in black and white, as can be seen I got the white model.

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The charger comes in a small box.


The box contained the charger, a car adapter, a universal voltage (100-240 VAC 50/60Hz) power supply, two spacers and a instruction manual.


The charger has two current settings (0.5A and 1A) with indicator leds and a usb out indicator led.
For each slot there is a red/green led. The leds are red when charging and green at other times.
This means that there is no error indication!

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The plus connection is slightly raised, this means that the charger can be used with flat top batteries. The slider only has a limited range, but with the included spacers it is possible to charge shorter batteries.


The minus connection is a slider. This gives a span from 46 mm to 70 mm long batteries, with the spacers one battery down to 31 mm or two batteries down to 39 mm can be charged. This means that the charger can only charge one 16340 battery with the supplied spacers.
This slider works smootly.


The charger has a polarity marking in each slot.


Power can be supplied from the supplied mains adaptor or from a car adapter.


Usb out power, this output has 5 volt when there is a battery in slot #1 and no power connected to the charger. The usb led will be lit when there is power.


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The charger can handle 70 mm long batteries including flat top cells.


Without power connected, channel #1 (USB output channel) draws 10mA from the battery, dropping to 3mA when voltage drops below 2.8 volt.
Without power connected, channel #2 draws 5mA from a full battery, going slow down to 3mA at 2.8 volt.
With power connected the charger will only draw 0.1mA from a fully charged battery.
Below 2 volt the charger will charge with 0.5mA, this is enough to reset a protection (Green led is on).
Between 2 volt and 2.8 volt the charger will charge with 150mA (Red led is on).
Above 2.8 volt the full charge current is used.
The charger will restart charging if the battery drops below 3.9 volt, after power loss or when a battery is put into the charger.
Two batteries in the charger will not change the charge current, i.e. the channels are truly independent.
Because each channel is independent, the different voltages and currents vary between the channels with a small amount.


The first test is with a 18650 battery, the charger does a CC/CV charge profile. The termination current is a bit high, this means that the batteries will be a few percent below maximum capacity.


Increasing the current to 1A makes the charging faster.


The charger handles a 18350 cells nicely, except for the high termination current. This means that less than full capacity is charged into the batteries.


It does charge my old 16340 cell, but the CV and final voltage is a bit low.



The second channel looks like the first, except a small difference in charge current.



Using both channels at the same time does not change the charging in any significant way.

Measurements on USB power

The charger can supply USB power while discharging a battery.

USB specification says the voltage must be between 4.75 and 5.25 volt, I have placed a yellow line at 4.75 volt in the charts.


The first test is with a 0.25A load. The output starts above 5 volt and drops while the battery is discharged, but it stays well within the usb specifications. When the battery drops slightly below 3 volt the usb output is turned off. The current drain is not turned completely off, the charge will continue to draw 3mA, this means that it is best to remove the battery within a few hours.


The output is rated for 0.5A load and can do that for about 3 hours with a 3400mAh batterry.


Trying to draw more than 0.5A (8ohm is 0.625mA at 5volt) does not work very well, the output voltage will drop below 4.75 volt after about 1 hour. This is, of course, perfectly acceptable for a output rated for 0.5A.


This charger does a good job with a CC/CV charge and the possibility to select two different charge currents. The usb out is also a good function.
I will call it a good charger especially for 18650 batteries.


The charger was supplied by Efest for a review.

Here is an explanation on how I did the above charge curves: How do I test a charger