It seems the closest way to doing this is to have the unit constantly on. I have thought about this and since I don't want the risk of not being able to start my car. My car has a GPS alarm which taxes the battery and I cant fit a bigger battery unless I relocated in the boot. It may suit you, I have to run it by dad as im not the best with electronics
This is what I have come up with:
-Cigarette +12v Accessories power to charger (use existing)
-
http://www.fasttech.com/products/1424/10003914/1280709
or
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http://www.fasttech.com/product/1280901
-3100 mAh Batteries $12 USD per pair or $11.44 with coupon code BLF
http://www.banggood.com/2PCS-NCR-31...anasonic-p-910641.html?p=PY1120374414201312TN
-USB to Mini USB 3m cable (ebay, pc shop, $1 shop etc)
Another cheaper option*
Premade 20000mAm $12
http://www.banggood.com/Wallet-Desi...ne-Tablet-p-79283.html?p=PY1120374414201312TN
or 30,000mAh $17.50
http://www.banggood.com/30000mAh-Ex...hone-MP4-p-916633.html?p=PY1120374414201312TN
*The latter 2 premade units come with some risk, they might be chinese mAh rated much higher then real world mAh. Also there is no info on the cells used so no idea of life, safety and it might be a false economy. I also have some concern about the output where users state they are not getting charge for tablets on the 1A outlet but works fine for 2A. I can charge my tab on a 500mA outlet on my pc. Charging a phone/tab is a lot less taxing then powering a dash cam.
I will probably go with the first option, I know it will output 2A which is enough for 2 cams to run off one unit, the Panasonic 3100mah is proven in terms of capacity and reliability and life, 4 of these will run a single 1a dash cam for over 10 hours straight. I read that the powerucc runs at 0.7A so expect a little more. They will also charge at 1A each so if you put it in your center consol, you can use a 2a adapter and easily remove (2 plugs) and put the batteries on a good charger overnight. The premade units cant do this and only charge 1a total
1A is Blue, this particular battery will go down to 2.5 however he didn't test it
another option would be this for $22 US if you want something simplier 10400mah $22 USD
http://www.banggood.com/Original-XI...e-Silver-p-923637.html?p=PY1120374414201312TN This uses LG 2600mAh Cells, I am confident that if they went to this expense that it should handle the 2A input/output stated. Although you cant take the batteries out like my preferred option you can still unplug it and use a USB wall or pc charger to charge it overnight. Not really a downside but the only one I would consider is that it will only do 8 hours @1A. After 6 months of daily use it might only get 7.5 hours so leaving it on at work it wont record the whole time. I would still consider this before the 2 cheaper options as you simply can not buy good bare batteries for what they are charging. e.g $23 US 4x 3100mAh (12,400 total) Pana or $36 for 4x 3400mAh (13,600 total) Panasonic (currently the highest real mAh battery available)