How do I automatically turn off my android tablet when battery is low I'm having problems with a android tablet that freezes when the battery runs low.
Is there an option in android or an app that could turn off the tablet when the battery is below a certain % of power left. Or that will turn the tablet off x minutes after last usage ?
There are several approaches possible. Some devices already ship with some kind of power management, which just needs to be enabled (check in Settings).

Apart from that, specific power management apps are available in the Playstore. E.g. Battery Life Saver can be configured to take actions on "battery low", like switching off WiFi, BT, and others (not sure if a power-off is included here as well). Big Battery promises to allow a shutdown at battery-low in its donate version.

And then there's always tasker to do things like shutting down the device at 20%, or shutting off WiFi etc. at 30%, and so on. As a free alternative, AutomateIt can do the same. But I'm afraid in both cases, this will require a rooted device.