For your information -- Interesting article.

Pete Woodworth

 - - - -

 [ from the LSC Winter Newsletter on web page
 [ "http://www.locationsound.com/97winter/battery.html"
 [ I think that the Denecke slate is a big audio console.
 [ Robbie

Battery Damage
by Ed Somers, CAS, Service Manager

We are seeing a rash of problems in our Service Department with
equipment that has come in with battery corrosion due to a battery
(or batteries) put in backwards.

Denecke Slates, PSC M4 mixers, and equipment using battery packs with
8 pen-light AA-cell batteries are the most common.  This is often caused
by inattention, rushing, or working in poor light.  Everyone should be
acutely aware of the terrible damage a reversed cell will cause in
electronic equipment.  I was curious as to how long it takes, and what
the mechanism is that causes the batteries to leak, so I contacted
Duracell via the Internet and asked them that question.  I was promptly
referred to an engineer to discuss the problem.

The information I received really surprised me.  First of all, when
a single cell is installed backwards the equipment will still work
because the overall voltage is reduced by only 1.5 volts.  Second, the
reversed cell is charged at whatever the current drain of the equipment
is.  You should be aware that alkaline batteries are not designed to
ever be charged.  What happens when you attempt to charge that battery
(by reversing it) is excessive gas pressure is developed within the cell
and very soon the pressure release valve built into the battery, and
every other alkaline battery, will open allowing the gas and the
electrolyte to escape.  The electrolyte is very corrosive to electronic
components and even anodized aluminum.  So how long does it take?

The answer to this question was the big surprise.  The engineer did not
have an exact time because the tests they did were at a higher current
rate, and he said that for lower current rates the time is not linear.
Their test was with 8 AA-cell batteries (12 Volts), with 1 cell reversed
and a current drain of 1.8 amps.  The reversed cell leaked in 4 minutes!
The Dance Slate draws 1 amp at high brightness; this means a reversed
cell will leak in approximately 10 to 12 minutes.  The average repair
cost on a Dance Slate with battery leakage damage is over $400.  So,
it makes tremendous sense to be very careful when making a battery
change.  Don't let anyone rush you.  Take your time and be careful.

 [ Alkaline dry cells designed for recharging used to be available,
 [ and I had good success in the 1970s using them in portable cassette
 [ recorders.  Good equipment which uses multiple cells will shut
 [ down when the battery voltage drops by the voltage of one or two
 [ cells, thus avoiding the damage described above.   -- Robbie