damn, sorry to hear! That sounds like a close call, and a bad time! Scary. Li-ion is sub-par for safety - I am not a fan of the old school tech.
How long did you have the battery on the charger? Did you remove it as soon as it finished charging?
My concern with these old batteries is that as they are all old stock (I think 2 years + at this point), the capacity is universally going to be lower than the already relatively small rating of 750mAh.
Overcharging is going to be quite easy, and using a unit that doesn't have ideal overcharge protection isn't best practice. I always recommended the Xtar MC2 for the hopper cells as I did an in-depth comparative look at the technical specifications of the recommended 3rd party option offered by HL (something from E-fest, renowned brand but with a US mains plug), the international-friendly USB powered Xtar MC2, and the much popular Nitecore D2. Of key interest is the amperage pushed post full charge detection, where the Xtar and E-fest excel with a very, very minimal current. The Nitecore D2 Charges with 0.2mA when LiIon battery is full. Xtar MC2 Charges with less than 0.005mA when LiIon battery is full. This is a considerable difference (~98%), and it really means that it is important to remove these old batteries AS SOON as the D2 says they are charged. They should not be left unattended, in that device - it will continue to charge them which is really terrible for any battery but the tolerances here are definitely questionable.
Not to assume that this is definitely the case, I am not going to claim to know the cause, but I can see that general battery safety at this point is worthy of some public scrutiny to a degree.
I did dig up this little analysis done on the GHB1's from yesteryear
https://www.reddit.com/r/GrassHoppe...per_ghb1_battery_750mah_bench_test_resultsan/
Very interesting charts, the guy who made them didn't know what the device was for, the testing is a bit arbitrary but quite insightful, it really is clear looking now that these cells are specifically designed for 45W draw. They are probably quite a volatile custom chemistry due to the power intent and from such a small package, this is why they are custom cells and you can't just expect to use any normal battery charger for custom cells. It has taken most of the life of the GH for this type of power draw to be available off the shelf (only caused by the
prevailing ecig market, being much, much huger - weed industry piggy-backing has begun to happen with the likes of the TUBO etc. but again, it's slow).
Shorting or failure will cause the battery to vent, and it is basically akin to a flare going off. We do not want 18650 size cells with this chemistry anywhere near our faces, not even in our homes, definitely not in our cars. Look up the explosion size difference between different size cells, and you will undoubtedly realise that these tiny cells were your saving grace Vapviking. The bulk of the phone in your pocket is made up of safety mechanisms for the archaic bullshit we push electrons with. The batteries are much safer there than the metal cylinders used everywhere else. The Note 7 battery incident is an interesting look at what it's like without those safety measures, and it's easy to forget what we are dealing with when it comes to commercial and niche products in the modern world.
A battery that is bulging or noticeably hard to reinsert into the Grasshopper (the GH batteries should fall into place freely with no resistance) is cause for concern, as is one that isn't performing healthily. Unfortunately that is really seriously all the batteries for this device in the wild right now. They need to be handled with extra care.
Everyone should heed this warning from Vapviking and be very careful with these things.
I'm so glad it didn't go off in your grasshopper, hand, or whilst you were away dude!!
I wish this grasshopper situation would just come together already, it's really sad history. I remain very hopeful, and very satisfied with my devices, but I wish it went differently, that I could see a different situation that was happy and content instead of hard done by, deceived and smouldering.
Come to think of it, the HL fast battery charger is going to need to be scrutinised to the highest degree as they haven't done good circuitry design anywhere else, or displayed any confident or semi-confident QC and it's their most dangerous item yet... should it ever exist