This sets the alarm threshold - the percent change from the battery's stored baseline internal resistance - that, once reached, triggers an alarm, per the description. Rising internal resistance is one of the earliest measurable signs of a failing lead-acid cell, well before capacity loss becomes visible, so this threshold converts a raw resistance drift into an actionable 'replace this battery soon' alarm rather than requiring the admin to interpret raw ohm readings. A setting of 020 (20%) means that once batteryResistanceChange later reads 20% or higher, batteryResistanceAlarmStatus would go active.