You go out in the morning and the battery is completely dead. Bone dead.
You gotta’ get to work and you don’t want to be late so you grab the jumper cables out of the trunk, pull your wife’s car up to the hood, and jump it off.
You only work less than a mile away. Everything seems to be normal, so you take off for work and probably won’t even be late. After work, you hop in your car, and although it’s not completely dead, it just doesn’t quite have enough juice to crank. Two weeks later your alternator pukes. What just happened ? Bad luck ?
Nope. You didn’t properly charge your battery and it beat up the alternator.
How DO you charge up a battery so you don’t hurt the alternator ? Set the charger on high for about an hour ? Nope.
The right way to charge a battery is low and slow. Trickle charge 12 hours is the best. You want the amps to go in and slowly fill the battery as deeply as possible, and this can only be done on the lowest setting your charger has. A high rate of charge will raise the voltage very fast, which will cut back the regulator in the charger and you will only get a surface charge.
And most of that will be lost when you run the starter 1 time.
Think of charging your battery, like you would fill a bucket with a little soap in the bottom to wash your car. If you crank the water hose nozzle wide open all you get is a bunch of suds. A couple minutes later, there’s practically no water in the bucket. But if you turn the hose nozzle way down, and slowly fill up the bucket, you get a full bucket, evenly mixed with the soap.