On Sep 12, 7:16 pm, Mark wrote:

OP, you need an accurate voltmeter.
If the charger pushes and keeps a 12 Volt battery voltage above about
13.6 v then it is "overcharging" it and reducing it's life.

Too high or too low a voltage will both shorten the shelf life of a
lead acid battery.

13.5 to 13.6 is about optimum for room temperature.

A good battery charger will regulate the voltage to that range.

Mark

Andy comments:
I can't disagree , in principle. However, this month the
temperature
in my garage ranged from 70F in the morning to 110F at 7pm....
Battery chargers or maintainers simply don't compensate over that
range.....
and the battery chemistry over temp and the component tolerances
in the "charger" both vary , and don't necessarily track over a wide
temp range....


Under the hood of an automobile, the range is greater , probably
from around 0F in the winter to 160F or higher in the summer..
The voltage "regulator" in the alternator has temp compensation,
but not for that great a range.... I keep an accurate digital
voltmeter
plugged into my cigarette ligher outlet and see the "charging" voltage
range from 13.5 to about 14.5 volts as the battery chemistry terminal
voltage
argues with the alternator regulator temp compensation from summertime
to wintertime.... That's why
car batteries only last a few years....

By the way, my voltmeter has headed off being stranded by a
dead battery several times as it lets me know when an alternator
diode has gone out, long before the charging stops altogether.
Plenty of time to fix the problem before the alternator has failed
and possibly the battery has sulfated.....Just a suggestion.

Andy in Eureka, Texas , P.E.