The way to get around needing the cell link is dead easy, buy a AGM battery 12 volt around 12-15ah or what ever you need, AGM batteries can be mounted in any position wired to dash cam lead/supply and given a live through a 5 pence 1N5408 diode so it charges AGM battery whilst in use, then when car is off AGM battery still continues to run cam, a 12 a/h will run a two cam set up around 24-28 hours, this size AGM battery will cost around £30 or so, I have fitted one under a front seat for some one, his car is used every day so 12 a/h was more than enough for him, totally leak proof totally safe, just need to put diode in correct way around so it charges AGM battery, for those with suitable space a normal lead acid battery could be placed elsewhere and wired the same, this will have no effect on the likes of cars with battery monitoring at all as it is effectively "unknown" by the cars electrical system.