Prius won't start humming whirling sound and rotten egg smell

Hi guys,
I just want to share my troubling experience which may be helpful.
One morning, I went to my garage and tried to start up the car and it won't start.
Before I got into the car, I've noticed a humming and whirling sound that is louder than the usual humming. The car was also emitting a weird rotten egg smell.
The panel lights came on, but seemed more dimmed than usual. I pressed the start button several times, but all it does is turn the instrument lights on and off.
I did a bit of research, and it ends up that I only needed to swap out the 12-volt auxiliary battery.
The battery is located at the rear passenger side.
Since my hatch door won't open without enough auxiliary power, I had to gain access to it by removing the cover to the spare tire. Once I expose the internal latch of the hatch door, I was able to lift a lever by the latch (just like the one for the hood) and push out and up to open the hatch door internally.
The 12-volt battery is fairly easy to remove.
I did not order an oem battery through the dealer; instead, I bought an Optima yellow top from Autozone (I don't work for Autozone nor Optima).
I think they last longer than oem, and they are immuned to drains.
It has been two weeks now and my prius is running like new.

 

Yes the vent tube was attached.
Yes, the smell came from the original battery which showed no sign of corrosion.
The issue occurred around 49,000 miles.
Also like to mention that about six to seven months ago we accidentally left the car on over night and found the car completely dead with no power the next day. We got a jump from AAA then it was running fine until recently. So, if a battery had been drained completely then the chances of it becoming cooked like mine is likely to occur.