What do the volts out of my battery charger mean?

by on March 6, 2013

Q: Battery charger voltage

Hi there,
I’ve been having trouble with the battery from my tractor and my old car this winter, and have been getting some very confusing symtoms when trying to recharge them.
Just out of interest, I decided to measure the voltage coming out of the charger.
It’s quite a beefy charger- one of those types that you can start the car with on it’s highest setting, and has three settings available:
Low, medium and starting current.
Here’s what I found:
On low setting it gives out 8.8 volts
On med it gives 9.7v
On starting 12.7 v.
Can somebody tell me what’s going on? Does this explain that when on low setting, no 12v battery I possess will get charged up?
Will I harm them by using the starting setting, so as to obtain 12 volts?
Many thanks in advance.