There's a lot of fake low grade batteries out there, so you have to be sure that it's an authentic LG.
Your mod could be defective and not charging right.
You could have simply hit a bad battery, so try the other battery that you have, as the way you said it, this is happening with just one that you've been using.
Most people will recommend an external charger, and so would I. I do charge via some of my mods, but I also have a charger for my spare batteries for my other ones.
I've also seen a few people have issues with Kanger mods, it's the type of "beginners" type that many get because they are a cheap/inexpensive kit, but most end up moving on rather quickly from them once they get a second mod. On my Facebook groups, lots of people end up selling them off cheap, as if just to get rid of them. So that speaks for itself to me. Whioe I had a Kanger tank at one time that I absolutely loved, at this time, I wouldn't touch any Kanger gear, I've seen just too many people complaining about them.
I now have many batteries, and learned that you need to stick with the better brand names (and ensure that you get authentic ones) as the secondary name brands are actually re-wrapped rejects/second tier from the brand names. Any battery from any that has "fire" in their names, the Aspire batteries, etc.
Out of my multiple batteries, I started with a few Aspires (as I wasn't aware of all this at the time when I started with the 18650 type mods and the store were "recommending them") and they have been the one "brand" that I've had a lot of issues with, with most of them dying very quickly, etc. I've switched to mostly LG 3000mAh ones (and some Samsung ones) and no issues with those.