Witschi Electronic Ltd Analyzer Q1 Page 31
16.7 Battery Testing
The voltage of watch batteries remains constant almost up to the very end of life and only falls
when the battery is completely exhausted. A test, even with a load, only shows whether the battery
can still be used or if it is completely exhausted. It is not possible to measure the remaining capacity.
Connecting the battery to a load resistor shows if the necessary current can be supplied without an
excessive voltage drop.
The
No Load
voltage is measured with a base load of 1 M that approximately corresponds to the
load from the IC current.
The
Low Drain
voltage is tested for 10 ms with a 2 k load resistor. This corresponds to the load from
a step motor pulse.
The test of High Drain batteries (batteries for high peak currents) is performed with a 100 load
applied for one second. This load approximately corresponds to the lighting of a LCD watch or to the
alarm function of an alarm watch.
To avoid testing the battery with an excessive load, the
High Drain
test is not automatically carried
out; it must be activated manually by pressing the start button.
The sealing of the battery must also be checked when carrying out the test. If salt crystals have
grown at the joint between case and back cover, it is necessary to replace the battery, even if its
voltage is still high enough.
Typical values:
Silver oxide batteries
No Load
and
Low Drain
voltage
Good battery: 1.45 - 1.6 V
End of lifetime: below 1.40 V
High Drain
voltage (only relevant for High Drain batteries)
Good battery: higher than 1.25 V
End of lifetime: below 1.20 V
Batteries for large watches (alkaline batteries)
High Drain
voltage
Good battery: 1.4 - 1.6 V
End of lifetime: below 1.20 V
Lithium batteries
As there are several technologies and application classes of lithium batteries, it is impossible to make
general statements.
The following values can be considered as typical values:
No Load
and
Low Drain
voltage
Good battery: 2.9 – 3.2 V
End of lifetime: below 2.8 V
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