Where does electricity go after being used?
Congratulations, you've uncovered the biggest scam of the 20th century.  Read this quick before the men in black come and get you.

Think about how AC power really works.  "AC" stands for alternating current, meaning it goes back and forth.  The power companies give you electricity on one half-cycle, then suck it all back on the next half cycle.  What a racket!

Seriously though, "electricity" is not a thing, more like a concept.  "Amount of electricity" is nonsensical babble.  You can have some specified amount of power, voltage, current, or other measurable properties, but not "electricity".  For those that don't fully understand current, voltage, and power, it is best to just avoid using the word "electricity" at all, since they'll most likely use it incorrectly.

To therefore answer your question, electricity doesn't "go" anywhere since it's not a thing or stuff that ever was anywhere in the first place.  Current and voltage together can be used to move energy around.  When a battery is powering your tablet, it is producing voltage and current, thereby transferring power from inside it to the outside.  The tablet uses that power to operate the computer inside, light the screen, transmit data over radio waves, etc.

Energy (and power, power is just energy per time) is not created or destroyed, just moved around.  In the case of the battery powering the tablet, the energy starts out in chemical form inside the battery.  It then takes on electrical form coming out of the battery.  The tablet uses it in electrical form, but eventually it gets turned to heat.  If you leave a tablet running just sitting there, you should be able to notice that it's a bit warmer than whatever it's sitting on.  The energy that was in the battery in chemical form is now in the stuff the tablet is made of in thermal form.  Eventually that will heat the air in the room, which will heat something else, etc.  By the time the relatively small amount of energy in a tablet battery is spread out over a whole room, you'd need sensitive scientific instruments to detect it.