I suspect that this model is particularly sensitive to having consistent/clean power delivered to it. When I was recently installing my 612GW I was fiddling with the settings with the engine/ACC off so I managed to accidentally discharge the battery. From this point the unit started to act up (even with the engine running) e.g. freezing up, refusing to format the card and it got VERY hot, once I'd put 25% charge back into the battery (USB charger indoors), the unit then behaved perfectly and has done since then (3 weeks).
The fact that the integrated better is such a low capacity probably doesn't help because it means it's easily discharged (and then the dashcam starts to throw a strop) especially when you consider that all batteries degrade over time and being exposed to direct sunlight through a windscreen is not an easy operating condition for a Li-On battery. Ultimately if a battery only has the capacity of the type supplied with cheap garden solar lights it doesn't leave much reserve capacity to cover battery degradation.
Personally I think it would have been much preferable to have had removable rechargeable batteries i.e. a proprietary battery pack where a replacement can be easily purchased or ideally just standard rechargeables i.e. 2xAA or a 9v, that way a user can choose to purchase the highest capacity batteries possible (if they so choose). The fact that you cannot easily purchase the integrated battery pack (in a unit that seems to often need the battery replaced less than every 12 months) seems like "built in obsolescence". It seems unfair that a user could have paid £250+ when the unit 1st launched, only gets a 12month warranty and once it's out of warranty has to bin the unit if/when the battery pack fails instead of being able to purchase a replacement pack and fit it themselves (assuming the user is comfortable taking the unit apart).
*To be clear, I'm really impressed with the overall performance of the unit but I believe companies should be called out in public for issues like the above. (Especially if they want to be succesful long term, they should properly address issues like this)