[R-390] OT; Battery Leakage

[Tisha Hayes]

Quote:
"They are supposed to have a shelf life of ten years, but some brands leak
far before the dc voltage drops off."
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That might be the kicker. When they give a battery a life expectancy it is
usually for a battery in its original package, fully charged and stored in
some place at 20 C.

As batteries dry carbon and alkaline batteries discharge they eat away at
the case. The case is the anode and the ions from the case corrode away and
migrate to the cathode in the center of the battery.

If you leave a battery installed in an electronic device like a Fluke meter
there is going to be a few microamps of drain on the battery. This is in
addition to any self-discharge that the battery already has going on.

If the battery is open-circuit and stored in its package the only leakage
is self-discharge, so that gradual migration of ions through the
electrolyte is what determines that 10 year life rating.

Putting any sort of load on the battery drains more off of the battery than
the self-discharge. That ten year life may now only be six months or a year
when that battery is installed in some device.

Remember that most power switches on devices this day actually do not
disconnect the battery. The power sense circuit is always juiced up.

It used to be that you could get an idea of where a battery is on its
life-curve by looking at the open circuit voltage. That is not necessarily
true any more. They have messed with formulations so a battery can have a
very flat performance curve until it just stops working, completely
depleted.

-- 
Ms. Tisha Hayes. AA4HA

*""It is not because things are difficult that we dare not venture. It is
because we dare not venture that they are difficult." -Seneca"*