This is exactly what has happened with mine!
I contacted nextbase about the "low battery" issue and they were little to no help, nothing about the warranty covers the battery; even the insurance I took out from amazon at purchase time won't cover the battery.
I've since thought 'to hell with it I'll use it as I can and get something different/better when it finally dies'. Well, before it's died it's killed my car battery. I too have the constant 12V in the power socket but I've never had issues with that, until now, I didn't use the car for a few days and in that time the battery in the dashcam must have discharged and recharged so many times it flattened my car battery - of course, at that time i didn't put two and two together, I just thought the car battery was faulty so I had it tested and it was fine. The weeks pass and it happens again, and again, then it clicks - it's the bloody dash cam! Unfortunately now my car battery will only just start the car and I've bought a jump start pack to support it (other reasons too).
Needless to say I don't have the dashcam plugged in anymore and most days my car will start fine, but the battery has been drastically affected by the dashcams issues. I'm going to see if I can get a new battery off the internet, hopefully a better one, and see how it goes but I suspect I may just have to wire it up without a battery (I'll go inside and whip it out and see what happens) and be done with it, crazy!!!
Any other thoughts of experiences with NextBase that suggest it's worth getting a better one - I have the 312GW so I thought I'd gone quite high quality? I can't believe NextBase had such a poor attitude to the issue, clearly there is one.
Cheers for your thoughts
P.S. I should add I've been through all the charging at home thing, resetting it, changing the sd card etc etc and no joy. It turns on then off again in about 2 seconds so battery is clearly fooked. It will be two years old this Christmas and I've had battery issues with it for the entire time, bar the first three months, but with it being plugged in I didn't see an issue.