I discovered 'Dashcam talk' through this thread, as my Nextbase 402G kept giving 'low battery' warnings and I googled for any advice.
As with others, it is about 12 months old and I couldn't find my receipt so considered my best action.
Having seen the relatively straightforward repair, I thought that was best, given the batteries are so cheap anyway.
As it happens, I had been in touch with Nextbase customer support and they kindly sent me a battery free!
However, the good news ended there...
I did indeed replace the battery, following the instructions here (the screws do actually hold the case together at the top). My doubts first arose, though, when I measured the voltage of the removed battery and found it to be 3.68v.
I thought, perhaps, that this was just not necessarily an accurate figure, as I believe that can drop considerably if the battery is failing and there is a current draw.
Unfortunately, though, the new battery behaved in exactly the same way.
It can be charged perfectly well using a USB, but does not maintain that level when plugged to the car supply, which is very curious.
Anyway, in the hope that the second battery may have been faulty too, I purchased a couple more through ebay (no guarantee of quality I know!) and tried them. No difference.
Again, the voltage was around 3.7v. I also measured the voltage when attached to a USB charger and it was barely 3.9v.
In the end, I simply bought a new cam but, out of curiosity, got in touch with Nextbase again. Their reply has left me stumped.
I asked what the voltage threshold for a low battery warning would be, as I would have assumed that if using a nominal 3.7v battery it would have been something like 3.0 - 3.2 at the worst.
Bizarrely, apparently the 'Technical Director' has said that the threshold is 4.2v!
I can't for the life of me imagine why they might use a step-up converter to get a higher voltage with just one small cell, if indeed they have, and I can't see how his information can be true using a 3.7v nominal battery.
Am I missing something here (I have a reasonable understanding of electronics, but wouldn't describe myself an expert), or is Nextbase doing something completely bonkers?
For my part, I suspect that the issue with this model of cam is not with the battery at all, but rather the charging circuitry and voltage threshold. I think if the charging is at too low a voltage then, while the cam is on, the available power drops too much to effectively charge. Then, because the threshold kicks in too soon and determines 3.7v is too low, the system switches off before saving the last file, which completely destroys the entire point of the camera.
I'd be grateful for a wiser and more knowledgable assessment, though, as I'm totally flummoxed!