[apwood]

I have a chinese mtk tablet running android 4.2.2 (not rooted)

I only use it as a satnav and nothing else. I use an external bluetooth gps receiver and might in future decide to use a bluetooth speaker. It has 3g that I use for traffic information. The satnav app I'm using is route 66 navigate and sometimes google maps.

To start up my satnav I run my bluetooth gps app and then start the navigation app.

It is left charging all the time I use it, so the battery is close to 100% most of the time.

When I'm not using it I don't want to shut it down, but I do lock the screen and unplug it from the charger. That way I can start my satnav quickly without having to wait for the device to restart.

So I need to minimise battery usage when the screen is locked, so it doesn't run out of battery whilst just sitting there doing nothing. Currently I'm trying greenify, but I'm not sure it's a full solution.

When the screen is locked, I need all running apps to be automatically closed (or at least the bluetooth gps app and navigation app), and bluetooth, wifi and 3g radios to be disabled, and the device put into low power mode (hibernation). The radios then need to be automatically enabled when the device is unlocked, and ideally the bluetooth gps app automatically started.

I don't mind using a homescreen shortcut or widget to do this, but I'm worried that any apps / widgets I install might in themselves use up the battery.

I've disabled background data (I don't need to sync or backup anything) - is there anything else I need to do to stop any background apps using the battery whilst the device is locked?

What's the best way to do all this?