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Opus BT – C3100 V2.2 Intelligent Battery Charger Review

Chargers do not last forever and using a mod as a charging device is not recommended. There are not the same protections with onboard charging as there are with an external charger. I always want to have a spare on hand so when I saw the Opus BT-C3100 V2.2 on sale at I had to get one.

The major improvements from the V2.1 model are the added fan and the automatic recharging function which eliminates the problem of discharging the batteries after a full charge. Charging is now activated automatically when the voltage in the battery drops to 4V. Also, the pre-charging function with pulse current is removed. This is done to prevent charging when the battery is inserted incorrectly into the slot. Previously, the device detected an inverted battery, as having a voltage of 0V (fully discharged and requiring precharge) and started charging it.

Let’s Dive Down

The BT-C3100 V2.2 besides charging, has a variety of other modes: Discharge, Test, Quick Test and Discharge/Refresh. Pressing the mode button will cycle you through these 5 modes.

Discharge/Refresh Mode:

This mode will make 3 complete discharge/charge cycles and will restore batteries that haven’t been used for some time to their rated capacity. This is a long process that can take from 8 hours to even a day.

Quick Test Mode:

The charger will measure the internal resistance of the battery by applying a load. The number on the screen is the detected voltage drop in milliohms. For good quality batteries the result will be low ( in the range of 20 ~ 80 milliohms). This is a 10″ process so it can be done a couple of times for more accuracy. Note that there’s around a 30 milliohms contact resistance from the charger itself that should be deducted.

Test mode:

Checks the present capacity of the battery by discharging it after a full charge. It first charges to 4.2V then automatically discharges to 2.8V and it displays the capacity value. The Opus then continues automatically to charge again up to 4.2V but retains the capacity value on the screen until the cells are removed. If the maximum capacity is much lower than the rated capacity, it is recycling time. I tested two “married” Sony VTC5A’s 2600mAh batteries. After almost 6 months of daily use the results are quite impressive.

Discharge Mode:

It is used to reduce the memory effect of Ni-Cd & Ni-Mh batteries (lithium-ion cells are considered to have no memory effect). The battery is discharged to a preset voltage (0.9V for Ni-Cd and Ni-Mh, 2.8V for Li-on).

Charge mode: 

The charging current, charging time, battery mAh and voltage level for each port are cycled on the screen when you press the display button. It will automatically stop charging once it’s done and resume when the voltage is under 4V.

Other geeky features:

There’s an internal switch underneath the charger where it allows you to change the maximum charging voltage from the default 4.2V to 4.35V or 3.7V. You don’t need to mess with that unless you want to charge and storage batteries at 3.7V, or you have cells that can be charged at 4.35V.

Another cool feature is that the BT-C3100 V2.2 can charge and discharge batteries of different types and sizes at the same time. You can choose your charging current from 200mA, 300mA, 500mA, 700mA ,1000mA and 1500mA/2000mA (on slots 1/4). The default setting is 500mA. The discharge currents are 200mA, 300mA, 500mA, 700mA and 1000mA (Li-ion batteries only). The maximum charging capacity is 20000mAh .

Overheat protection: 

The BT-C3100 V2.2 is equipped with a temperature controlled cooling system. When the internal or the battery(ies) temperature is over 40°C the fan will be switched on. If it reaches above 60°C all 4 slots will be automatically halted. The charging /disacharging process will only resume after battery temperature drops below 40°C.


The Opus BT-C3000 V2.2 is a great investment. It’s a well built charger and works as expected. The sliders in each slot are smooth and firmly hold batteries in place while charging. It’s got a nice bright display that lights up the minute you add batteries. Being able to choose the charging current, test and refresh your cells is a big plus. In fact it is the biggest advantage it has against its competitors at that price point. The only con I have is that the fan is a little bit loud when it turns on. All in all this is a versatile piece of hardware that I highly recommend.

Opus BT-C3000 V2.2 specifications

Compatibility: AA (LR6), AAA (LR3), NiCd, NiMH and 3.7V Li-ion rechargeable batteries in size of 18650, 14500, 16340, 10440, 10340, 18650, 20700, 21700, 26650, 26500 17670, 18490, 17500 and 17335.
Charging Cells: 4
Input Voltage: AC 100~240V 50/60HZ
Output Voltage: DC 12V, 3.0A
LCD Screen: Yes
Circuit Detection: Yes
Protected Circuit: Yes
Short Circuit Protection: Yes
Over Voltage Protection: Yes
Over Charging Protection: Yes
Over Discharging Protection: Yes

Package weight: 0.602 kg
Product size (L x W x H): 14.40 x 9.80 x 3.90 cm / 5.67 x 3.86 x 1.54 inches
Package size (L x W x H): 16.00 x 22.00 x 5.00 cm / 6.3 x 8.66 x 1.97 inches
Package Contents: 1 x Opus BT – C3100 V2.2 Intelligent Battery Charger, 1 x Power Adapter, 1 x English User Manual
The Opus BT-C3100 is available at

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