Lamar Technologies D-1560 - Manual (Page 4)

OPERATION PREFACE CONTINUED
The only practical way to test this capability is with a constant current load.
By the end of one hour under the battery’s rated one-hour capacity
(amp-hr capacity), the battery voltage must not have dropped below the assigned
cut-off voltage which, for a 24 volt battery is usually 20 volts.
However, in normal usage over time, the actual capacity will be lower than
the rating, and both the military and FAA allows an acceptable value of 85% of the
battery’s nameplate ampere hour rating. This can be 85% of the one hour rating at
full load (e.g. 51 minutes at 40 amps for a 40 A-H battery with acceptable end
voltage of 20 V or higher), or 85% of current for 60 minutes (e.g. 34 amp for 60
minutes).
There may be other acceptance criteria such as ½ of the AH rating for 2
hours, and battery end voltage being 18 volts.
For ratings of batteries higher than the 62 amp limit of the 5160 tester, the
acceptable discharge time is extended in scale with the battery rating. (e.g. For a
120 amp-hour battery, set the test current to 60 amps and run test for 2 hours).