The discharge capacity of a lead acid battery varies and is dependent on the discharge current. LCB valve regulated batteries used to rate at the 20-hour rate. i.e.: The capacity of the battery at 20 hours discharged to an end voltage of 1.75 V/cell at a temperature of 25°C

General Comments
The discharge curves show the minimum design parameters for each fully charged LCB battery size after installation. Full capacity is reached after some initial service.
Float Service: One month after installation and recharging.
Cycle Service: Within three to five cycles after initial charge and service entry.

Technical Terms
1. Battery capacity for small valve regulated lead-acid batteries (VRLA) by accepted convention worldwide is described in “AMPERE HOURS” at the 20-hour rate (C20) when discharged at 25°C. E.g. a SP7.2-12 is 7.2 Ah at C20 that is the battery will deliver 0.36 amps current for 20 hours to a cut off voltage of 1. 75volts per cell (10.5 volts per battery).

2. Battery load, by convention is described in terms of a multiple of C, in amps, where C is the capacity atC20 e.g. for a 7.2 Ah battery. 0.05C is 0.36amps. the final discharge voltage is at 1.75V/cell. Below is battery discharge current and final discharge voltage chart.

Discharge current (A)
Final discharge voltage(V/cell)
0.2C>(A) or intermittent discharge
0.2C≦(A) ≦0.5C
0.5C≦(A) ≦1.0C
Discharge current (A): 0.2C>(A) or intermittent discharge
Final discharge voltage(V/cell): 1.75
Discharge current (A): 0.2C≦(A) ≦0.5C
Final discharge voltage(V/cell): 1.70
Discharge current (A): 0.5C≦(A) ≦1.0C
Final discharge voltage(V/cell): 1.55
Discharge current (A): 1.0C≦(A)
Final discharge voltage(V/cell): 1.30

3. Battery cut-off voltage is the volts per cell to which a battery may be discharged safely to maximize battery life, this value is specified according to the actual discharge load and run time. As a rule of thumb high amp loads and short run times will tolerate a lower cut off voltage (e.g. 3C at 1.3v/c), whereas a Low amps long run time discharge will require a higher cut off voltage (e.g. 0.09C at 1.75v/c).

Over Discharge
When one battery is being deep discharged, the voltage under load to go below its cut-off (or “final”) voltage of a full discharge, it is defined as over-discharge. It is important to note that deep discharging a battery at high rates for short periods is not nearly as severe as discharging a battery at low rates for long periods of time.