(Review) Opus BT-C3100 V2.2 NiMH-NiCd-Li-ion Battery Charger

The opus BT-C3100 V2.2 is an intelligent 4 slot lithium-ion battery charger with a easily readable backlit LCD display. This charger supports up to 2Ax2 or 1Ax4 charging current. The BT-C3100 is a great choice for charging multiple 18650s at once and especially testing different cell’s capacitys with its numerous functions.

This charger can be found on amazon for $37.99


Specifications Listed by Manufacturer

Main Features:
The charger integrates the minus delta voltage for NiCd or NiMh battery charging termination, and for Li-ion batteries charging to 4.2V with pre-selected constant current. ( 3.7 Li-FeO4 and 4.35 type high voltage batteries charging mode can be selected through switch on board )
Easy to read LCD with back light Showing Battery Voltage, Charge / Discharge Current, Charging Time, Battery Capacity etc.
Operating temperature: 0 - 40 deg.C
Max charging capacity: Up to 20000mAh
Power adapter: DC 12V, 3.0A ( Output ), 100 - 240V, 50 / 60Hz ( Input )

  1. Voltage update rate is 30s instead of 60s.
  2. 4.35V charging time can be very long because charging current is regulated in entering the CV stage at 4.12V, which is same as 4.2V type. Now
    3.35V charging algorithm is changed to 4.27V.
  3. New fan cover make better protection for cooling fan.
  4. Charging current range ( mA ): 200, 300, 500, 700, 1000, 1500, 2000
  5. Discharge current range ( mA ):200, 300, 500, 700, 1000 ( li-ion cell battery only )
  6. Max. charging capacity: 20000mAh
  7. Voltage deviation: max 0.03V 4.2V
  8. Current deviation: max 5%
    Type: Charger
    Brand: Opus
    Model: BT-C3100 V2.2
    Rechargeable Battery Qty: 4
    Input Voltage: AC 100~240V 50/60HZ
    Output Voltage: DC 12V, 3.0A
    LCD Screen: YES
    Auto Circuit Detection: YES
    Built-in Protected Circuit: YES
    Over Voltage Protection: YES
    Short-Circuit Protection: YES
    Over-Charging Protection: YES
    Over-Discharging Protection: YES
    Battery Quantity: 4


Package weight: 0.558 kg
Product size (L x W x H): 14.4 x 9.8 x 3.9 cm / 5.66 x 3.85 x 1.53 inches
Package size (L x W x H): 16 x 22 x 5 cm / 6.29 x 8.65 x 1.97 inches


1 x Opus BT - C3100 Battery Charger
1 x US Power Adapter
1 x English User Manual

Included AC-DC adapter outputs 12v 3A Max

Physical Attributes

The Opus BT-C3100 is made out of ABS plastic and feels like is has a very sturdy structure and is built well. The buttons below the LCD feel very solid and have a nice click to them when used. The charging bays adjustable negative poll is attached via spring which also is very strong and holds the battery in place very well.

This charger holds 4 18650 cells comfortably and is very easy to extract them from the bays when they are done charging. Protected versions of all compatible cells fit snugly inside the charger except for protected 26650’s.

The negative end of the cell is just barely not connecting thus the problem with this charger and holding protected 26650’s

Cooling The unit
The charger has a cooling fan built in to cool down the internal components when charging at high currents
The fan is somewhat loud but not loud enough to be bothersome when in listening vicinity

The unit is approximately 4”x 5.75” or 10cm x 14.5cm

Display and Selectable Modes

The BT-C3100 has multiple different modes (Charge, Discharge, Test, Quick test, Refresh) and charging currents to choose from including 200,300,500,700,1000,1500,2000 mAH

Operating the Unit
Pressing the mode button will cycle you through the 5 selectable modes (Charge, Discharge, Test, Quick test, Refresh)
Pressing the display button will cycle you through the 4 different informational displays (Voltage, Current, Capacity, Charge time)
Pressing the current button will allow you to select the desired charging/discharging currents
Pressing the slot button will cycle through the 4 slots in the charger




Charge Time

The Modes

The unit has 5 selectable modes including Charge, Discharge, Test, Quick test, and Refresh.

Charge Mode: The rechargeable battery is charged up to its maximum capacity. Accumulated charging capacity is displayed at mAH display mode.
The charger will charge 4 cells at once charging each at 1 amp. But if you are charging only 2 batteries you should put them in the outer slots (slots 1 and 4) to increase the charging rate to 2 amps a piece. This is especially good for charging 2 26650’s at the same time

Discharge Mode: Discharge mode is used to reduce memory effect, The rechargeable battery is discharged to a preset battery voltage (0.9v for Ni-Cd & Ni-Mh, 2.8v for Li-ion batteries). Once discharge is finished, total accumulated discharging capacity is displayed at mAH display mode.

Refresh Mode: The rechargeable battery is charged and discharged repeatedly to optimize to its maximum capacity. Old rechargeable batteries or rechargeable batteries that have not been used for a long period of time can be restored to their rated capacity

Test mode: Checks the present capacity of a rechargeable battery. The maximum capacity is determined by discharging the rechargeable battery after it was fully charged.

Quick Test mode: The charger will analyze the dynamic internal battery resistance by applying a load and the current reading is referred to the voltage drop detected on the battery. Within 10s, the tested battery resistance will be displayed in the unit of milliohm.

Supported Batteries/ Technical Data

This charger can only hold 2 26650’s in the outer slots

Final Thoughts

The Opus BT-C3100 V2.2 is a great all around charger option for all those who want to charge multiple cells at a time and for those who want to test the capacities of their cells. This charger can be used by anyone with any experience level due to the simplicity of the operation of the device. My favorite aspect of this charger is its ability to discharge your cells to get the exact readout of mA to see if your cells capacity is infact true to what the label says. The charger also fully charges all cells to a even voltage of 4.2 volts and trickle charges them to keep the cells topped off if you leave them on the charger after they are done charging.

The only thing I would have liked to see in this charger would be a higher charging current when charging 4 cells at a time, especially for high capacity 18650s it will take about 3.5 hours for them to fully charge at 1A

All in all I highly recommend this charger to anyone who wants a well built, multi mode charger that will act true to its specifications.

nice review, these can fully discharge protected cells?

Thanks, it will drain protected cells as low as the protection circuit will allow

So I guess you can’t really tell the true MAH of a protected cell, as I doubt you could get it to zero? Good to know, all I have are protected batteries

Nice review! just ordered one.

I have this charger but when performing a discharge test it stops at 3 volts sharp. Did you experience different behavior with your specimen?

Yup, mine stops at 3v too. Opus is due for an update with this charger. It’s been over two years with this 2.2 version. I bought mine Dec 24 2015, and the v2.2 had already been out a while.

There are features they need to add like a storage function for all 4 slots, where it charges or discharges to 3.7v then stops. The resistance is wildly inaccurate, redesign the case so it fits four 26650’s at one time, lengthen the slot so it fits protected 21700’s, needs a better fan, and a few other things.

AFAIK, the Opus BT-C3100 does trickle charge Li-ion cells (as said in the conclusion of the OP), which would be a bad thing. When the batteries are full, the charger stops charging entirely and only when the voltage falls below a certain value it starts charging again, and so on.



It already has that ability, but you have to get at a hidden switch on the bottom of the mainboard. I cut a small hole to access it with a probe. Works fine. You can also set it for higher voltage cells that way. Also works fine.
Resistance could be better, but it does sort of work. It seems to be better on the Zanflare C4. I’ve found a ‘reasonable’ correlation between the Opus and Zanflare IR. No good at all on the Lii-500-should be improved or removed.

If you want to go through the hassle putting in a superior fan isn’t too hard.
I also use a 5A laptop power supply for mine. Overall I think it’s my best charger now, certainly the most versatile, especially when I want higher charge and discharge features. The C4 and Li-500 are much more limited there.

I think the IR accuracy depends on the unit, the care in placing the cells, AND the quality of the cells seem to affect it….a lot. Decent cells seem to have ‘reasonably’ consistent readings. As the cells become more degraded, meaning higher IR, the readings show MUCH more erratic readings and less consistency. OTOH, that shows the cells are going to hell, so it’s still useful info. :slight_smile:

Because I will put in an 18650 to charge and it will say for example, 90. Take the cell out and put it back in the same slot, it will read 53, take it out put it back in the same slot it will read 125, and so on. And many other have reported the same thing



I have a hole cut in mine as well, for the occasional 4.35v setting. But that flimsy little switch is likely to fail. They need a slot selection setting for storage. Yes, they need to update the fan, and that was the other thing. 5A power supply needs to be included. And you still can’t fit 4 26650’s side by side.

It’s been 2+ years. They need to update this stuff

I’ve tried cleaning both terminals on the charger and both ends of the cell. Seems to make no difference. All 60 of my lithium ion cells are inside the same room with the charger, inside the house. So they are all the same temp.

So what irks me is that no one can keep milliamps and milliamphours straight,

“charging currents to choose from including 200,300,500,700,1000,1500,2000 mAH”
“to get the exact readout of mA to see if your cells capacity is infact true to what the label says.”

both should be the opposite, good day.

I'm running the test/discharge on two 26650 protected batteries at .5A and the fan does not come on with my opus. Is that normal? I thought fan should come on when discharging.

Did the fan turn-on when plugged? It should run when plugged, then turn-off.

The fan is temperature controlled. It will only run when the factory calibration for temperature threshold is reached, and run only when the threshold is reached.

I don't know if it came on when I first plugged it in. Good to know it's temp controlled thanks. I may take the risk and let it run as long as things don't seem to get too hot and when the test cycle is finished I will make sure the fan turns on when plugged in.

Anyone know where I can get a 12v car adapter to fit the opus charger?

It uses DC 5.5x2.1mm plug, isn’t it? Maybe something like this will work:


(it indicates up to 1.5A only though, which may not be powerful enough if charging at full speed)

I noticed the BT-C3400 comes with a car charger plug and was hoping to get that one as it looks a little more sturdy.