Update:

My friend brought his truck with a bigger battery and jump started it - it worked!
BUT, as I was driving it to the shop, the car died. At first the wipers were going really slow.. Then I kept getting error messages of the 4x4 being out of order, transmission failure, airbags turned off etc... Such a panicking moment. Slowly everything shut down. Luckily I was able to pull over safely.
Called a tow truck and took it to the shop. It's most probably the alternator in this case. But I know for fact that the battery was weak too. Maybe it's them both combined? Or maybe the battery has always been good, but the alternator kept sucking all the juice out of it?
Anyway, I'm changing all of them. Not gonna pull up with any more headache.