Yaris breakdown : Engine starting issue

[talhahs]

I left my office, reached parking area and my Yaris wont start. I parked it around 8:30 AM and tried turning it back ON at 5:30 PM.

On moving the key, dashboard didn't light up. I realized there is something wrong with battery..horn too didn't sound powerful. Hence, I got it working after connecting the booster cable with the other battery. Now the strange part is as soon as I leave my foot off the accelerator pedal, rpm goes down (either in N or D) and it stalls and finally goes OFF (in 2-3 seconds). I got it back ON with booster cable 6-7 times but every time leaving it foot-free gets it stalled and engine OFF. With foot ON, engine got warm and no sign of issue.

Battery connections are tight and no sign of salt/anything..

What could be the reason of this problem? Another thing I was observing from a while that in N position with no foot on pedal, it used to slightly get stalled i.e. flickering of ODO backlight as if engine wud go off, engine rpm going down (below 500), etc but never got OFF. Everytime I used to accelerate, it got fine, ODO backlight solid

Please share what cud be the reason of this issue...my Yaris still parked at office...