If you use mods with any kind of replaceable batteries, then you are going to need a good battery charger. Today thanks to GearBest - Best Gadgets & Electronics Deals I will be reviewing the Opus BT-C3100 V2.2. For over 3 years, I have been using a 4 slot battery charger, the JetBeam Interllicharger I4 Pro, it has served me well & it is a good charger, handling battery sizes from 26650 to 10440 & everything in between. It also handles NiCad, Ni-Mh & Li-Ion recharging needs & is able to charge all three different types of batteries at the same time, when I have had occasion to utilize this feature, it has worked flawlessly, all my batteries charged properly & no mishaps. So why then would I want to replace a very good battery charger , that handles a variety of cells? The answer to that could be a variety of reasons & the Opus BT-C3100 gives you a variety of reasons to like it over a good but basic charger. Unboxing: The BT-C3100 comes in a nice protective box, the box itself gives you a good idea of the BT-C3100's capabilities. Inside the box, there is the BT-C3100 wrapped in a bubble wrap bag for added protection, the manual & the power pack. Taking it out of the box we can see the BT-C3100 more clearly & that the included power pack has a Euro or perhaps US plug, thankfully GearBest provide a plug adapter free with your BT-C3100, so you will be able to use it when it arrives. However, as you can see in the second picture below, the length of the plug, with the included adapter attached is quite long, while the power pack is not overly heavy this is not the ideal way to plug in a power pack. Buying a power pack with the same rating as the included one, with an AU plug is the best solution for this, just be sure the plug into the charger is the same type too or using one of these Buy Multi Reverse Travel Adaptor | Read Reviews | **** Smith Online Shopping as I am, which has a recessed section on top, providing better stability, works well too. Features: The Opus BT-C3100 can do all the things my old JetBeam charger could do but it has added features & improvements over the JetBeam. Where the JB had 4 slots for charging batteries, it only had 2 charging channels, this means that when charging 2 batteries in the same channel, the rate of charge to each batt is halved & it will take twice as long to charge that pair. So in effect to charge batteries at the fastest rate only 2 batteries at a time could be charged. The Opus BT-C3100 can charge all 4 batteries at the maximum rate & adjusts that maximum rate according to the type of battery it senses in each slot (NiCad, Ni-Mh & Li-Ion). In other words, this charger has true 4 channel charging, unlike the JetBeam or Nitecore I4 Pro chargers(which are virtually the same as each other, the JB has a few minor advantages). The charging ranges from 200ma up to 1000ma, from what I have experienced. The manual that comes in the box says that the charging range can go as highs as 2000ma but I have not been able to test this with the batteries I have charged in it & I would not want to charge them any higher than at a 1000ma rate anyway. The next feature of this charger is overheat protection, when the heat from charging reaches a set temperature, the BT-C3100's built in cooling fan kicks in, to dissipate heat. I have seen & heard the fan working & it is not at all loud, it is a feature most battery chargers do not have but one I think is very good to have. It also has: 5 different mode settings (more about these below). A LED display for each slot, which can be changed between Volts(how much charge on the batt), mah(the measured mah in the battery since charging began), ma(the current the batt is charging at) & Hours (the time in minutes/hours that the battery has been charging for). Selectable current setting, for each individual slot. A slot button to toggle between slots or select all slots together. The LED display is back-lit, when a button is pressed & stays lit for 20 seconds. By using the mode switch you can select between the 5 different modes, which are: Charge - Already discussed. Discharge - I have not used this mode but it says that it is used o reduce the memory effect some types of rechargeable cells can get & give back more usable capacity to the cell. Refresh mode - Again I have not used this mode, it says the battery is charged & discharged multiple times to optimize its capacity (useful for old cells or cells that have not been used in a long time), this process can take days. Test mode - The charger will first charge a battery fully, then discharge the battery fully(to 2.8v on a Li-Ion cell), to determine the current health (mah) of the cell. This is a really useful feature, it can tell you which of your batteries are well below their rated maximum mah & even confirm that you have new batteries that have been rated correctly (incorrect mah rating can be an indication of fake cells). Quick Test - Another very handy feature, this will tell you the internal resistance of your battery in milli-ohms, a high internal resistance indicates a poor cell, which would not be suited for vaping purposes. The charger in use: The spring slider contacts are smoother & not quite as tight as the ones on my old charger, this makes it less of a possibility that they will be used as slings for my batteries, if my hand slips while inserting them, a nice improvement over the old charger. The display is uncomplicated & easy to understand, well lit (when a button is clicked) & has nice big numbers which are easy to read even from a distance. Charging is simply a matter of inserting a battery into a slot, if you touch nothing, it will use the default ma setting for the type of cell inserted & start charging (for 18650 Li-Ion this is set at 500ma). If you want to charge the battery faster or slower, you have 10 seconds after inserting it to start to change the current (ma) at which the cell will be charged, simply by clicking the "current" button until the desired current is found. Most chargers do not tell you how much charge has been put into your battery, the Opus does, when you put a completely flat cell into the charger & it cycles to full, you can check the mah on the battery. This is particularly useful for vapers to know. When your batteries are new, they will have their maximum mah, as they get used & go through charge cycles that mah capacity diminishes, knowing how much charge is in your batts will give you an indication of how long the run time of the battery will be. It also gives you an indication of how hard the battery has been pushed over time & when it may need replacing with newly purchased batteries. This combined with the quick test function, could save you using tired old cells & running out of battery power when you are not at home & away for hours at a time. The one little quirk that this charger has, that I am not completely certain of why it does it, is it will charge a 18650 battery fully, to 4.2v, then if you don't take the battery off the charger immediately, it will drop the charge down slowly to 4.16v. I suspect it does this for safety, so that the battery does not over charge, which is obviously a good thing but it is also a little annoying having to take the battery out & watch as it charges the cell up to 4.2v to get full capacity from your battery. I do not know if my old charger did this, because it had no display & instead used LEDs to indicate charging or full. It is both a comfort & an annoyance, to know the Opus does this, 4.16v is not a lot of difference to 4.2v & in real terms it is probably about 2 or 3 puffs on a PV anyway but I do like my batteries fully full. Overall: At around $35US from GearBest, here: Opus BT - C3100 V2.2 Li - ion Digital NiCd NiMH Battery Charger ( EU Plug )-34.18 and Free Shipping| GearBest.com the Opus BT-C3100 V2.2 is money well spent, GearBest also have the JetBeam or Nitecore I4 Pro for around $20US, if your budget is tight. If you can afford the extra $15US, the Opus BT-C3100 is highly recommended, for less than double the price you are getting more than double the charger. There are many other chargers on the market but chargers as packed with features as the Opus BT, generally cost a lot more. Only time will tell if this charger lasts as long as my old JB has but the construction & safety features, plus all its other features, have me thinking it will & that it will be a very long time before I need another battery charger.