Aux Battery - why won't it keep my Nexus 7 from draining its battery?

[prof_rosewood]

I use my Nexus 7 with an aviation app. I have a dry cell 12v battery that I plug the Nexus into but the main battery still drains. Any ideas on why or other ways to add an aux battery?

 

[GSDer]

Welcome to the forums!

Am I missing something about your setup? None of these devices use 12V - they're all expecting 5V, and some current load from 500 mAh to 2A. And even that doesn't guarantee that the charge will keep up with the discharge rate - it's pretty common for a device running a CPU/graphics intensive application to continue to discharge (albeit at a slower rate) while connected to a power source.

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[prof_rosewood]

I am sorry for omitting the fact that I attached a cigarette adapter then plugged in a usb adapter that outputs 5v. It doesn't keep up with the drain. The battery is a 12v 7amp hr.

 

[GSDer]

Ok. You'd have to look at the output rating for the USB adapter that you're using - it could be anywhere from 500 mAh to 1A. Even at 1A there may not be enough juice to keep the tablet from discharging.

Do you have the GPS turned on?
Is Wi-Fi on?
Is the screen brightness at full?

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[cab2]

Use this, it even works with N7 wireless charger in my car.

Amazon.com: PNY P-P-DC-UF-K01-GE 12 Volt 2.1 Amp Rapid USB Car Charger - Black: Electronics