Battery jumps from 25% to 2% to 36%. What's going on?

I have a 2012 13" Macbook Air running 10.9.5. I seem to be losing battery life as of late. This, itself, isn't a huge deal, as I usually use the laptop near an outlet, but as of late the more annoying problem is that it doesn't know when it's about to be fully drained. Often it just goes into instant sleep around 20%. I go find the power cable, plug it in and then it shows it was actually at 0%. It's as if it just can't "see it coming" anymore.

Today, the oddest thing happened. I saw it jump from 25% directly to 2%. This triggered me to go find the power cable and I was able to plug it in at 0% before it went to sleep. As soon as I plugged in the cable, it jumped to 36%.

What is this a sign of? It seems more software related than hardware, but I really don't know.

Is this a hardware issue worthy of a trip into the Apple Store? Or is this something I can some how 'reset' myself?

The most annoying part is the battery just not knowing when it's about to force my machine to sleep. If I can fix that, even with shorter battery life, I'd be thrilled.