Battery jumps from 25% to 2% to 36%. What's going on?
I have a 2012 MBA as well.

The battery is still doing it, at 510 cycles now.

In your case try the SMC reset to fix that problem.

If you hold the "alt" key then click on the battery, it will give you some information including what is consuming it.

If you open the Activity Monitor in your Utility folder, then click on the Energy tab, there will be a display of Battery performance for the last 12 hours: