User Guide

TROJAN BATTERY
26
9.5.Discharge Testing
î Follow the procedure below to determine battery capacity.
î Ensure the battery set has been fully recharged before testing.
î Prior to running a discharge test, ensure that all charging sources and loads are disconnected from
the batteries.
î Connect and start discharger.
î Record the runtime (minutes) when discharge is complete.
î Correct runtime minutes for temperature using one of the following formulas*.
o For temperature measurements in Fahrenheit
M
c
= M
r
[1 – 0.005 x (T
1
- 80)]
o For temperature measurements in Celsius
M
c
= M
r
[1 – 0.009 (T
1
- 27)]
Where M
c
= Corrected discharge time corrected to 80°F (or 27°C)
M
r
= Recorded discharge time
T
1
= Battery temperature at end of discharge (°F or°C)
î If the corrected discharge time is greater than 50% of the batteries’ rated capacity at that discharge
rate, then battery performance is considered acceptable.
î Restart the discharger to record the individual battery voltages while still under load
(current being drawn).
î If the discharge runtime is less than 50% of the batteries’ rated capacity, the battery with a voltage
that is 0.5V lower than the highest voltage may be a failed battery.
o There are other methods of testing batteries including internal resistance
(i.e. C.C.A. testers) and carbon pile discharge testers. However, these are not
suitable testing methods for deep-cycle batteries.
*These formulas are only valid for battery temperatures between 75°F (24°C) and 90°F (32°C).