Heat and moisture- the two biggest enemies of electrical devices. Dust and tin whiskers a close third. Chinesium is especially vulnerable. That clearly overheated. Don’t know if that was a defect or could have been avoided with a fan, but I don’t take chances as far as airflow goes.
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Thanks @anon70102222
Yes I was using a fan. (For the heat issues) This time I was charging a 21700 and unplugged the unit since I was going out. When I got back, I plugged it back in and that’s when they popped/blew. So im guessing powering it on with batteries installed caused a voltage jump. Maybe has something to do with - the unit being able use it as a power source running from the batteries to charge other things via the USB port. Im guessing it took the 12v and added the 3.7-4.2 volts from the battery when it powered on and blew the circuits.
Here’s the transformer that sits right under that Pc board. It’s massive. 
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Sorry if an external fan was already mentioned. I admit, I don’t always fully read threads with such long-keyed posts.
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Yea sorry you have to use a fan also… It seems such a bother for something as simple as charging batteries.
Have you ever powered off the switch on your power strip and then turned it back on when batteries were in the unit? I don’t recall reading that that was a NO NO, But that’s what caused the problems both times. Like a power spike issue
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I don’t know if I need one. I choose to because sometimes I’m paranoid.
I guess it’s like any accident. Your brakes fail because they were close to worn out and you put it off and you hit a tree. Or, you change your brake pads a little earlier than needed and your brakes don’t go out and you don’t hit a tree. Was the early maintenance the reason you had a normal day, or was it just fate? Who knows, because an accident that never happened is sort of hard to quantify. My chargers are alive after 4 years. Luck, or the fan? Got me.
But I like my fan.
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I’ve been using a D2 for 3 years now with no issues, or excessive heat. But, only 18650’s.
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I have (out of habit) specifically avoided doing that (powering up charger when one or more batteries are installed in the unit). When a “classic” (capacitive energy storage) power-supply is powered up, discharged energy storage capacitor(s) represent a maximum current load to the circuitry, also resulting in maximal (input to output) voltage-drops across active semiconductor devices within the circuitry. Such is the scenario where energy-storage capacitor (and perhaps semiconductor) failures are historically most likely to occur.
A charging battery cell looks (electrically) much like a very high Farad value capacitor. The lower the charge of (and associated voltage-drop across) the battery cell(s), the more (possibly) dangerous the situation (may) be. Modern switching supplies operate at high frequencies, reducing such concerns considerably. However, energy storage still takes place (in capacitive and/or inductive components), and the magnitude of voltage drops (and perhaps current-flow maximums) associated with (battery loaded) power-ups may (in a poorly designed battery-cell charging system) exceed rated semiconductor device voltage/current limits.
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I’ve been using 25R’s for a while on regulated mods, I am rarely exceeding 10 amps and very pleased with the time they provide. I generally swap them out for freshly charged batteries when they are about 3/4ths of their maximum discharge. I have some around that are still charging up to 4.2V at three years of age (well over the hypothetical 300 or so charges most 18650’s are supposed to handle). The only other batteries I find that provide longer vaping time are HG2’s but they are also rated at more MAH. Just picked up some 25r’s from IMR - at under $3.00 per, you can’t beat them.
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As detailed in a previous post, the mAH capacity that is available from Samsung 30Qs and 25Rs differs only by ~100 mAH when (due to requirements of many regulated devices, it appears) they cannot be utilized below 3.3 V (adding less than 200 mAH when used to 3.1 V, and adding ~300 mAH when used to 2.9 V). When pressed, I am able to utilize my Sigelei 30W Minis and Eleaf Pico 25s down to (around) 3.1 Volts. The above pertains to 5 Amp continuous discharge. 25R can handle slightly higher discharge currents than 30Q.
Nevertheless, this old miser (who sometimes obsessively savors every last electron-charge), is phasing out 25Rs and phasing-in 30Qs. One (possible) advantage is that IMR’s 30Qs provided over the last years time are manufactured at a plant in Korea, whereas their 25Rs are manufactured at a plant located in Malaysia.
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I had one i4 that crapped out and another i2 that was my first charger when getting into vaping. Since then I purchased an Efest LUC Blu6 (which died in a month but was replaced by Efest) - since receiving the new Blu6 several years ago, and using it daily, have never had a problem. I rarely use the bluetooth but it’s nice to have and something to play around with till the novelty wears off (like in a week).
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For those who like to charge batteries when not present, and/or when asleep or otherwise less than fully conscious, I would wait for these little darlings to (also) come out with a (“futuristic”) Bluetooth interface:
Source: https://world-of-heli.de/en/media/images/lith-ex-feuerloescher-lipo.png
And don’t forget to also invest in “My Little Elf” AI Blue Robots to faithfully “point, pull lever, and pray”. 
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It’s neet to see what everyone is using and doing.
OK so IMR they only refunded 1 of the units, didnt refund shipping, or even bother to say sorry for the ruined warps and messing up one of the new 21700’s I just bought from them. Luckly I was able to recover it on the 3rd attempt Seems ok for now. Also re-wrapped the 3 - 21700’s with some custom stuff.
I was using 18650’s on a single battery mod, and just got fed-up (even used HG2’s) So since it also took a single 21700. Im digging the extra amp power and life from the 40t’s
Guess now I head over to www.18650batterystore.com/dealoftheday.asp and spend money there now. Honestly any company that says they don’t support vaping with their products. (like I saw other say in this thread from IMR) Thats 2 strikes for them right from the start for me to drop from my vendor list id buy from. But keep posting I love reading your stuffs and seeing your pics. 
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It appears to be the battery manufacturers (as opposed to individual vendors, save for the IMR terms and conditions agreement also applying to Molicel brand batteries) who “will not support” customer usage of their (unprotected) Lithium-Ion batteries for “vaping” applications. Thus, vendors cannot seek reimbursements.
Seems that my 3M Adhesive Packing Tape “instant-wrap” solutions cannot compete with your “wraps”. 
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@Raven-Knightly
Noticed that IMR voids out Molicel’s offer even when Molicel offers support.
Hea man… Buy the clear wraps 10pc for 99cents and I’ll make any art work you want. Been sticking to B&W for now personally But I’ll hook ya up with the art with crop marks to cut.
Just drop them in a word doc print and cut em. Just remeber to put one upside down if you want them to line up. Since on most dual mods the batteries go in 1 positive up and 1 positive down.
Or you can DIY Specs are
18650
Width
18mm x3.14 = 56.52mm Final Dimensions 2.23inch or 668 pixels
Height
65mm = Final Dimensions 2.56inch or 767 pixels
21700
Width
21mm x3.14 = 65.94mm Final Dimensions 2.59inch or 776 pix
Height
70mm = Final Dimensions 2.75inch or 824 pix
Single 21700 color
3 designs for 2 x18650 each![18650 Battery|375x500]
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About the Opus, I can confirm that each battery slot has its own fuse.
One of the older Opus’s slot blew a fuse when I put a battery upside down, and did not affect the charging in the other slots.
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I’m using the Nitecore NEW i4, charges everything, going on 9 months heavy use never had an issue. Also use a Efest Pro C2 just for 18650’s
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I’ve had that same charger for over two years now, use it every single day
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ditto… think mine is about 3 yrs old now… I can even plug mine into my car… for camping! 
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You can never be too prepared!
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