I looked at the comparable Ipad and that has a a 7000mA battery which takes 2.1A at 5V to charge. This is quite large so actually I would only risk charging a couple of times. A car battery usually has 70Ahr and the ipad uses 5v so assuming some losses in the usb charger (converts 12V into 5V) you need about 1.25A at 12V for 4Hr to charge so you use 5Ahr, so 3 charges would drop the battery 20%. I wouldnt go much lower than that. An iphone has 5x less battery capacity so you could get 15 charges before I would worry.
Charge it when you go out in the car, even if its just nipping out to get milk.
I think the Powermonkey will be used for the phones and I will always charge the Tab on the move but know I can probably do at least one complete charge from a stand still.
We use a 12v inverted in the car, it charges nearly everything we have quite efficiently. To be honest you wont have any problems using your car.
The alternator on your car charges the battery right from the word go, and alternators kick out of lot of power. You can have a a dead battery and charge it running around using the alternator. Every time you move the car the battery is charging from it.
If you have a diesel car the batteries tend to be bigger still and more like a leisure battery. You could charge everything you have and the car would be alright for a few days. Using my inverter we've charged smartphones, sat navs, laptops, cameras, battery packs nearly everything.
I tested charging the tablet on my way to work this morning and in 35 mins it increased the battery from 77% to 89% with everything still left on.
That will be fine I'm sure.
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Topic: Tablet charging from car
