How can you tell if a battery is about to kick the bucket?

[John Suter]

Hi Steve,

> I have two identical buses. One bus has
> steady voltage almost
> always and the other varies from about 14.5 volts to
> 12.5 volts.

A fully-charged, good, 12v battery "at rest" will
generally indicate 12.65V. The inverter/charger can
be "set" (for the type of coach/house battery - Gel,
AGM, Lead-acid) to absorption/acceptance charge at
14.1v or 14.3v, and to float about 13.1-13.5V. Is it
possible your 14.5 and 12.5 readings are the result of
checking when the charger is activated and not
activated (or immediately after charging but not
really "at rest" some several hours later)?


> I
> can't figure out where the voltage draw is going. It
> almost acts like
> some as large as an electric cooling fan is coming
> on, but these buses
> have hydraulic fans. And the other bus never shows
> syptoms like this.

As others have already suggested, the only real way
is to "load test" each individual battery, not the
entire bank. A load test device can be characterized
as the inverse operation of a charger - the charger
brings the battery up to say 14.3, stops its charging,
and the battery "rests" back down towards 12.65. The
load tester virtually "dead shorts" the battery
momentarily down to say 11v, stops the "short," and
measures the immediate voltage rise back towards 12.65
and the time (in seconds) it takes to return.
Oversimplified, a poor battery sluggishly, or never,
returns, while a good battery "springs" quickly back
toward the initial voltage. A good load-tester
actually performs a more sophisticated set of tests;
but you get the general idea.


> So I'm wondering...is one of my batteries
> about to die? I've
> heard the lead plates inside can "almost" touch, and
> cause problems
> since they're almost a dead cell, so is there any
> way I can test these
> batteries or do I just have to wait 'til they drop a
> cell?

The best way to get the most life cycles from any
battery is to "maintain" them. In general, maintain
lead/acid batteries by keeping the water/acid level
above the top of the plates and keep them well
charged. For AGM and Gel, charge them relatively
slowly and often. AGM/Gel lives are measured in terms
of charge/discharge cycles - e.g. the less-deep their
discharge before their re-charge, the more times they
can be "cycled" before their life is exhausted.

John Suter


__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com