Battery problems

I have a second gen MBA that's getting close to 4 years old. Earlier today I was using it, and immediately after waking it up from sleep the fans went crazy, iStat Pro told me that the temperature was 85C. After a few minutes of that the temperatures were going down, but the computer suddenly shut off and wouldn't turn back on.

I took it back to where I had the power adaptor and tried turning it on with it plugged in and it worked, but said the charge was 0% while I remember looking at it shortly before it turned off and it was around 40%. Also I'd been watching the battery health on iStat pro since I know it's holding a lot less charge than it used to, and it was at 84%, but after it switched off and I turned it back on the battery health had dropped to around 50%. After using it briefly on the battery and then plugging it back in iStat Pro has said the health went back up to 84% though.

Anyway, what my question is, is there something going on here besides just the fact that it's an old battery that is getting close to needing replacement?

GGJstudios said:

It may, indeed, need replacement. How many cycles are on it? You could try resetting the SMC, but it may or may not help. The link below should answer most, if not all, of your battery/charging questions. If you haven't already done so, I highly recommend you take the time to read it.

Apple Notebook Battery FAQ​

Click to expand...

It says 834 cycles, so I've known for a while that it would need replacement soon, I was just expecting it to continue going more gradually than what happened today.

I guess also a bit of what I'm worried about is having heard stories about batteries blowing up I'm just wanting to make sure with it doing that suddenly there isn't something bigger wrong with it than it just being an old battery that doesn't hold a charge well any more.