We've (well me anyway) all hit the kill switch and left the ignition on. It is like boats, you have to launch with the drain plug out at least.
Been there...done that on both...and other learning opportunities. BTW...I also put my gas cap on my seat on a paper towel. That way I know when I forget to put it back on.
As far as changing batteries: I have tried to make it a practice to change out my batteries on my various vehicles at 3 year intervals. They all eventually go, and today's technology seems to go from working one day to dead the next with no slow decline. Its a lot cheaper and convenient to buy a battery from my supplier of choice and install it in my garage.
It is like boats, you have to launch with the drain plug out at least.
OUCH! That one hit home!
ANYHOW -
Can't tell you how long it would take to recharge a SEVERELY DISCHARGED battery with a 1.5A charger, but, if you killed it completely you may not be able to recharge it. Beyond a certain point you will a kill a battery. DEAD! MUERTO! ADIOS!