10 −15 amp is a good size charger.
No, you can not charge a 3V battery with 12V charger.
can a 12v lawn mower sealed battery be charged with 12v battery charger use on cars
No
No.
No
NO, voltage of the charger must match the battery voltage.
The meter on your battery charger will be in the green
Yes, the amp hour rating gives you an idea of the capacity of the battery and charger. The charger and battery need to have the same voltages. i.e. dont try to charge a 6v battery with a 12 v charger. The battery will be charged until it is full.
Depends on the amperage of the charger. A 10 amp charger will charge it in about 1 hour.
yes
No, you need a 24 volt charger.
No, you must use a 14.4 volt charger.