Hard to say. It should have a decent charge in 6 hours if the battery is good.
can a 12v lawn mower sealed battery be charged with 12v battery charger use on cars
No, you can not charge a 3V battery with 12V charger.
If it is totally dead charge it for 2 hours at 10 amps.
Depends on the amperage of the charger. A 10 amp charger will charge it in about 1 hour.
That depends on the amp-hour capacity of the battery.
Depends if its a 6V or 12V battery. If its a 12V battery, us the charger in the 12V setting.
Till the battery is fully charged. -Could be 4-12 hours.
A good auto battery will hold it's charge for at least 6 months or longer.