09 GT randomly has no electrical power

[projectr13b]

So this is an odd one. My initial thought was "oh shit, my battery died, I must have left a light on or something over night", but I checked everything and it was all off.

Mods: Eonon head unit, ultragauge.

Turning the key to accessory I get no power to anything. It's like the battery is unplugged. I jump it, car starts right up with no issues, so I'm positive the issue isn't a bad starter at least. Seems like it would be just a dead battery, but early while waiting for my roommate to come jump me, I had left the key in accessory. All of a sudden, all the lights and everything come back on. Go to start the car and nothing, everything's dead again.

I've seen quite a few posts about either a bad battery, or the immobilizer, or a key needing reprogramming, or the battery in the key fob being bad. Haven't seen anything describing what happened with the car's electrical turning on then shutting back off like mine did though, so I'm looking for anything else that I should maybe check.

Key Fob has a relatively new battery. I only have 1 key, so I can't try a spare unfortunately.

I'm going to go get the battery and alternator tested on my lunch, but any other ideas would be helpful.

Thanks

[projectr13b]

Nevermind. Seems like it was a loose connection to the positive battery terminal. Odd that I've had no issues for 2 years, but I'd rather it be something stupid like this than an actual electrical issue. Will update if it turns out to be a bigger issue than that.