Charger AV4m+


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This charger is a bit special, orginally it is from a brand called MEC, but the German company accu-select modifies it significantly and then add a + to its name (or a s for the model with serial data output). The modified model name is not printed on the charger, but only visible in the documentation and the listing for the charger. The charger is an analyzing charger.


I got the charger in a white cardboard box with very little text on it.


The box contained the charger, a power supply and a car adapter, manual is downloaded from the internet and is in German.


There is some sort of manual on the bottom of the charger, but it is for the orginal charger, not this modified one.


Power input is a 12V barrel connector.


Charge current is select with this switch, actual current will depend on cell size (From manual):
AA: S:540mA, M:800mA, L:1030mA
AAA: S:210mA, M:310mA, L:400mA
Changing current during charge will trigger a pause on the charger.


The user interface is the display, 3 buttons, the current select slider and a buzzer. The socket on the top is for serial data, on the + model it can be used to update the software in the charger, on the s model it can be connected to a computer for data logging.
Button functions:
CAP: Recall discharge values
DIS >2sec: Start a discharge, charge function.
SEL+DIS >2sec: Start a charge, discharge, charge cycle (CDC).
DIS >4sec: Cycle the batteries until maximum capacity is reached.
CAP+SEL >3sec: Enter setup mode, mostly sound configuration, but it also include voltage calibration.

The buzzer in the charger is used to signal a lot of stuff and has many different sounds patterns

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During power on the charger will do the usual display test and then show the software version.

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The display will usual change between voltage, time and capacity. To make the sequence easy to read a U is displayed before the voltage, i.e. the sequence contains four steps: U, voltage, time, capacity.
Pressing the CAP button will immediately move to capacity display, in the discharge modes it will be discharged capacity.


But there is also a couple of other messages that can be displayed, like the "HOT" message above.

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The charger has basically two separate battery holders, one for AA and below that one for AAA.


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This function is automatic started when batteries are put into the charger.


Nice charging with -dv/dt termination, but why do it charge twice. After a 10 minutes rest it start charging again and again terminatates nicely.
This pause is part of the charging algorithm used by the charger, the display will show PAU during the time.
Display shows 1.48 volt, 2:09 hours and 2.22Ah, the time is actual charge time with the pause subtracted.


The other 3 channels works the same way.
Display shows for #2 1.47 volt, 2:05 hours and 2.15Ah
Display shows for #3 1.50 volt, 1:55 hours and 2.04Ah
Display shows for #4 1.48 volt, 2:06 hours and 2.17Ah


With medium current setting it works the same way.
Display shows 1.48 volt, 4:46 hours and 2.21Ah


And also with small current setting.
Display shows 1.49 volt, 4:29 hours and 2.37Ah


With all 3 high capacity cells the charger terminates nicely and then has the extra charging cycle.
Display shows for XX 1.47 volt, 2:44 hours and 2.82Ah
Display shows for powerex 1.45 volt, 2:47 hours and 2.87Ah


The AAA cells are also terminated perfectly first time around (and also second time).


At the low current setting the charger is a bit slow to terminate, but it is still acceptable.
Display shows 1.48 volt, 4:32 hours and 0.95Ah


Charging 4 cells at full current is a problem, due to heat. The charger takes a break to cool down, before finishing the charge (It would have been slightly faster to use medium mode).
Display shows: 2.24Ah, 2.44AH, 2.48Ah, 2.29Ah


Using my power supply it can be seen the charger uses about 1.1A at 12 volt. This time it had to pause twice due to heat.
I am a bit suspicious about the pause implementation, it always happens during the final charge, where the batteries do get hot, maybe the temperature limit is a bit too low.


M1: 42,6C, M2: 41,8C, M3: 39,9C, M4: 36,2C, M5: 53,8C, M6: 45,2C, M7: 45,0C, HS1: 75,7C


The charger needs a long time to start, after about 10 seconds it has passed initialization and shows the animated charge icon, but it takes about 15 seconds more before the actual charge starts.


The charging is only about 75% of the time, the last 25% is a measuring pause.


The measuring pause is held at different times for the 4 channels.


The slider will change current immediately, but the software will not allow it and stops the charge for some time.


Trickle charging is done with pulses 0.75seconds wide applied each 65 seconds, this means about 15mA in average trickle current for L setting.


To activate this function the DIS button must be pressed for >2sec.


Discharge is done at about 500mA and followed by a charge.
Display shows 1.48 volt, 2:09 hours and 2.22Ah (Charge values)
Display shows 1.21 volt, 4:23 hours and 1.92Ah (Discharge values)


The discharge current is not affected by the selected charge current, only the included charge is.
Display shows 1.49 volt, 2:40 hours and 2.14Ah (Charge values)


The heat from the discharge is not that bad, but the following charge needs a pause.
Display shows: 2,29Ah, 2.52Ah, 2.49Ah, 2.30Ah (Charge values)


M1: 31,9C, M2: 30,5C, M3: 29,5C, M4: 28,3C, M5: 46,1C, HS1: 70,4C

The reason batteries stay cool during discharge is because the heat is dissipated as far away from the batteries as possible (Very nice).


The charger does also stop for measuring during discharge, but not as often.

Charge, discharge, charge (CDC), i.e. a single cycle

To activate this function the SEL+DIS button must be pressed for >2sec.


This function is for capacity measurements and will first charge the cell, then discharge while measuring capacity and finally charge again.
Display shows 1.47 volt, 2:11 hours and 2.25Ah


To activate this function DIS must be pressed for >4sec.


This function will discharge and charge batteries a couple of times, until the capacity do not increase anymore.
Display shows 1.47 volt, 2:19 hours and 2.22Ah


Usual I do not check analyzers fully for precisions, my standard charge/discharge test is only within 3% and with pulsing current I cannot guarantee the result will even be that precise.

This time I took a cell and cycled in all slots, then discharged it on one of my electronic loads (500mA current) and finally cycled in slot #1 again.


The results looks good, the charger shows very consistent results. The slight drop in discharge capacity is probably due to the cell

Testing the mains transformer with 2500 volt and 5000 volt between mains and low volt side, did not show any safety problems.


This is an interesting charger with lots of functions. The functions are the same as other analyzing chargers, but without the pwm regulation. The lack of pwm regulation limits the available currents, I do not really see that as a problem for AA and AAA cells.
The compact size of the charger and no fan means it has a heat problem when charging four cells at full current, the charger can easily handle it but the charge time is longer.
I do not like that the charger charges each cell twice, it is probably related to "Nachlade-Kontrollen", that is supposed to get the maximal capacity from the cell.

It is a fairly good analyzer and it looks like the precision in good and probably considerable better than most other analyzers.


Charger was supplied by Pro backup ( from

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