Exide Technologies Section 92.30 - Manual (Page 14)

9.6 EFFECTS OF FLOAT VOLTAGE
Float voltage also has a direct effect on the service life of your battery. A float voltage above the
recommended limits reduces service life. The chart below shows the effects of float voltage
(temperature corrected, see section 9.1) on battery life.
For example: A battery has a design life of 10 years, but the actual annual average float voltage is 2.33 volts
per cell. The projected life of the battery is calculated to be 5 years [10 years - (10 X 0.50) = 5 years].
Voltage records shall be maintained by the user in accordance with the maintenance schedule published in
this manual. To obtain the optimum service life from the battery, it is important to make sure the batteryʼs
float voltage is within the recommended range.
9.7 OHMIC MEASUREMENTS
Impedance, resistance and conductance testing is collectively known in the industry as ohmic
measurements. Each measurement is derived using a manufacturer-specific and proprietary algorithm
and/or frequency. This means that one type of measurement cannot be converted or related easily to
another.
“Reference” ohmic values are of dubious value because so many factors can affect the way the readings
are made and displayed by the devices. Connector configuration and AC ripple as well as differences
between readings of temperature and probe placement will prevent the ohmic devices from generating
consistent and meaningful data.
It is best for users to establish their own baseline values for their battery as specifically configured.
Do not rely on reference values.
If users wish to enhance normal maintenance and record-keeping with ohmic measurements, GNB
recommends the trending of this data over time. Use a first set of readings taken 6 months after initial
charge and installation as the baseline data. Subsequent measurements should be taken using the
same device over the life of the battery. Because cell positioning within the string (connector
configuration to a particular cell) can affect the reading, always compare each cell at baseline to itself
in the new data. Stand-alone ohmic data is not sufficient to justify warranty cell replacement. Responsible
ohmic device manufacturers acknowledge that there is no direct relationship between percent ohmic
change from baseline and battery capacity. A change from baseline of 25% or less is in the normal noise or
variability range. Changes between 25% and 50% may call for additional scrutiny of the system. And an
IEEE compliant discharge test is usually warranted on systems exhibiting more than a 50% change from
baseline. Consult a GNB representative for specific questions about ohmic data.
Percent
Reduction
In Battery life
0%
50%
75%
Temperature corrected 25°C (77°F)
Float voltage per cell
Minimum Maximum
2.25 2.30
2.31 2.35
2.36 2.40
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