On 11/26/2014 08:30 AM, KenK wrote:
While trying to come up with something more to worry about, I thought of my
backup battery. I have a 12 v deep discharge lead acid battery with a
Battery Tender wall wart charger. I check the battery water level monthly
(usually) and keep an eye on the charger indicator light. I see no problems
but wonder if there was an easy way to be sure the battery will be charged
when the power goes out and I need it for a light and, if summer, a fan.
Just trust the charger to detect a problem and warn me by changing the
light color or blinking? An easy test of some sort, other than turning the
light and fan on for a half day or so every few months? I suspect I'll just
have to take my chances.

TIA







1) You should not be charging a "wet" type lead acid battery in-doors,
the hydrogen emission is explosive. The type of battery you should be
using in your house would be VLRA. (Valve regulated lead acid.)

2) Since most people ignore my first point when I warn them, the type of
charger you use /can/ make a difference. Ideally you'd want to employ
hysteresis-loop charing techniques. This type of charger only charges
between preset voltage ranges and minimizes water consumption and
maximizes battery life. You are unlikely to find such a charger in the
"consumer" market...so the next best thing is a "float" charger which
will retain a constant voltage just below the battery's gassing point.
What you do not want is a "trickle" charger. That type simply puts out
an /unregulated/ small amount of current.

3) There are testers that can check a battery's internal resistance
without actually putting a load on it. They are fairly reliable but the
only sure way is to actually load it down. A reasonable test would be to
simply place a heavier than usual load on it for a relatively short
period of time and check the voltage drop. If the battery can stay above
11 volts under a heavy load it's probably fine.



Additionally: If you do insist on using a "wet" type battery my advice
would be to /not/ keep it on charge. Unless there is a load on it, it
may only require a "top off" every three months or so. The charging area
should be well vented.


My credentials:

I worked for Enersys as a Senior Service Engineer & retired after 38
years. Many a time have I seen exploded batteries and I did so myself
exactly once.