Congratulations! You can finally stop looking for an AA/AAA Battery Charger. This Opus BT-C2400 charger redefines the term ‘Smart’ charger. Others make claims and either fall short, or fall way short. I’m a techy geek at heart and so when my recent smart charger died, I was off on a journey. I really liked the last charger and was thinking to just simply by another. I then went to the internet and found that they no longer make it, and, the failure I had seen with that design had a common problem (overheating). I then invested about 2 weeks of ‘free nights’ reading, and reading… about all the features of modern chargers. Let me share some very important results of that time and batteries.First, let’s talk about what we are charging. ‘The’ batteries to buy are Eneloop brand which are a premium brand of the low self-discharge type. These batteries hold their charge much longer than traditional NiMH batteries. I use them in remote controls, calculators, and all those other devices that need to hold a charge for more than a few months. One thing though, these great batteries do not like heat. If you treat Eneloop batteries correctly, they can see as many as 2100 charges. So if you get the right charger and batteries, this is a great low cost investment and also a very kind thing for the earth (stop buying those alkaline batteries that go into the trash). I have two young children that commonly forget to turn things off, so being able to put the batteries back on the charger is very welcome. Sadly, if you research enough about most of the chargers out there, they have what is called ‘trickle charge’. After the batteries are charged most of the way, then they are pulsed with a light amount of current to keep them topped off with power. That sounds good, right? Well… sort of. Most of these chargers charge far too high of a current (around 100mA or more). If you leave the batteries in the charger by accident for a few days, you can already be damaging your Eneloops. OK, so best to have no trickle charge or low trickle charge (less than 20mA). The Opus BT-C2400 charges most batteries I have around 7-14mA. This is very very low… a great compromise between topping them off and keeping them full all while not overheating and killing your batteries. While I would suggest you do remove them after charging, there should be no harm if left in the charger for a bunch of days.Next, it is essential to have a good display to see what is going on with your batteries. Many chargers have pretty icons just showing a battery slowing filling up or overly simple green/red light. This tells you almost nothing. Ideally, you’ll know the voltage, the current, the capacity of the batteries and to see all that information for each charging slot. This is again another area where chargers fall short. Here the Opus BT-C2400 does a fine job.. (see pictures of this various screens in action) with information at your fingertips.Many chargers do an OK job with fresh batteries and yet most also do not do well with older batteries. As the batteries get older, their internal resistance increases and their capacity decreases. Many charges will just blink or say ‘null’ and not even attempt to charge older batteries. The blinking can get pretty darn frustrating when you are left wondering ‘now what’. No matter what you do, most of the chargers just won’t even try charging. There are tricks you’ll read about tricking the charger to charge the battery with using a paper clip to jumper the output of a good battery with an older battery. Just Google “null” and paperclip and you’ll see what I mean. But who wants to spend this money and do sketchy things with paperclips… doesn’t sound too safe or good to me. Can’t chargers just be smarter? Well this is probably the most important feature of the Opus BT-C2400. I’m an engineer and we talk about algorithms, these fancy mathematical formulas that make all the math inside these chargers work. Important to know, if you buy the BT-C2000 model, you might get the less optimized firmware. If you buy the BT-C2400, you’ll get the latest firmware/algorithms. The Opus BT-C2400 is monitoring the specific properties of these batteries and adjusts the current to accommodate each batteries health. See video that shows this charger set at 1000mA and yet it sees two older batteries (marked #1 and #2) charging at lower current instead of the dreaded "Null". This allows charging of less than optimal batteries of which all my other chargers won't charge. Also, it keeps battery heat much lower. Simply put, it charges batteries other chargers won’t. This was the primary decision maker for me! If a charger is full of great functions and display but can’t charge batteries... then the rest wouldn’t matter.Speaking of features – I insisted to have Modes to not only charge the batteries, but, also give you an idea of the overall condition of them (diagnostic modes). We don’t want to fill our earth with all these batteries that were thought to be bad due to poor battery chargers. The C2400 can measure the capacity (Charge Test) and internal resistance (Charge Quick Test) and these values can tell you when it’s time to finally recycle the batteries. Even better, there is a specific mode called Discharge Refresh. The charger will cycle a few times charging and discharging in an effort to bring life back to aging batteries. I highly suggest you occasionally use this feature even for ‘good’ fresh batteries, to extend their life. It is always best to deplete a battery before charging and such modes as this will do that and more.My old charger was compact, I thought that was so nice. When narrowing down the search to the last few chargers, I thought I was going to miss how nice and compact since most were significantly larger. Many of the modern chargers charge a huge variety of batteries both NiMH, LiPo, Lithium Ion, NiCd, etc. To accomplish this, there are these spring loaded trays for the batteries. I already have an excellent one like that. It hooks to a computer, can output results in Excel, etc. It has far too many features that I’ll ever use and most of all, getting batteries in it is not fun. It ends up being this balancing act holding batteries just right and letting these sliders pinch the batteries holding them up in the air. Often the battery’s weight is such that the battery can fall out. I expect that most of you will be charging AA/AAA NiMH batteries and if so, this is the Opus BT-C2400 is perfect. If you absolutely needed to have a charger for mixed types such as NiMH, NiCd, Lithium Ion and sizes beyond AA/AAA, then there is the big brother charger the Opus BT-C3100. However, since I use AA/AAA NiMH, I was happy to skip the C3100 and go straight to the C2400. That charger has no sliders and instead dedicated slots that you can effortlessly load AA/AAA batteries into. Also, I learned that I now LOVE the larger charger. I had become accustomed to having to sneak batteries out of the old charger and not pop out the others that were still charging. The old compact charger that I thought I loved, well… I don’t miss it. The larger Opus BT-C2400 allows me to remove a battery in the middle with little effort. It’s a dream.This charger handles all the batteries up to 1000mA. However, a nice added bonus, if you use the outer only two slots, you can actually charge up to 1400mA. It pays to read the instructions! So if you are in a hurry and only need to charge 2 batteries, you can sneak a little extra power into the batteries to speed up charging. This brings up something that I could not research online but had to test myself. Battery temperature with higher current settings. On my last charger, the batteries got hot… sometimes even scary hot. This Opus charger, on any setting so far, the batteries don’t get even close to hot. Batteries being a little warm is very normal for all chargers. With the Opus, the batteries are nearly room temperature most of the time. As said before, this means the batteries will live much longer (many years).I was not given a unit to review, was not paid, nothing. I just fell in love with this charger so much and was so happy that I felt compelled to share this experience. I hope this review will save some folks the many hours of research and nearly 100 chargers I looked at. BTW, I also bought a second charger because I loved it so much. I suggest any of you who are looking for an AA/AAA NiMH charger look no further. Buy some Eneloops and this charger and save the planet of the alkalines eating up our landfills.