l
cells and note if there are any cells much lower than the others. Amy
cells having a specific gravity of 30 points lower than the average
will generally be found to be in trouble, unless these cells happen to
be low from having had spillage in shipment, replaced with water.
(This condition, however, should not exist in future installations if
the spillage is properly taken care of, as has been explained on page
482.)

Voltage Readings

After taking a specific gravity reading, a voltage reading of each
cell should be taken. Voltage readings taken on open circuit are of no
value, so while taking these readings the battery should be on
discharge, having at least a discharge of 15 amperes. A good way to
get this discharge is to hold the starting switch in and set mixing
valve lever at lean point or wide open.

A low or defective cell will show a voltage reading .10 to .20 volts
lower than the other cells on discharge, while a reversed cell will
show a reading in the reversed direction when on discharge, especially
on heavy discharge.

The voltage readings are a sure check if taken in connection with the
specific gravity. When you have low specific gravity and low voltage
on the same cells, it is a sure indication of low cells. These cells
should be inspected for the probable cause of their being low.
Shorting of the lugs at bottom of plates and moss bridging across at
bottom of the elements, or possibly a split separator, will generally
be the main trouble.

When any of these conditions exist, it is best to take the low cells
back to your shop for repairs.

When there is absolutely no indication why the cells are low, they can
be cut out of the battery on discharge and put in on charge, until
they come up.

The following is a good example of readings taken on a battery with a
10-ampere discharge and having four low cells, 4, 8, 11 and 16. The
battery had been giving poor service, due to insufficient charging:

Cell No. Specific Gravity Volts
1 1.200 1.98
2 1.180 1.95
3 1.205 1.98
4 1.150 1.75
5 1.190 1.95
6 1.195 1.98
7 1.200 1.98
8 1.130 1.70
9 1.200 1.95
10 1.205 1.98
11 1.100 1.40
12 1.190