Lead–acid batteries designed for starting automotive engines are not designed for deep discharge. They have a large number of thin plates designed for maximum surface area, and therefore maximum current output, which can easily be damaged by deep discharge. Repeated deep discharges will result in capacity loss and ultimately in premature failure, as the disintegrate.
How deep should a lead acid battery be discharged?
The common rule of thumb is that a lead acid battery should not be discharged below 50% of capacity, or ideally not beyond 70% of capacity. This is because lead acid batteries age / wear out faster if you deep discharge them. The most important lesson here is this:
What is the nominal capacity of sealed lead acid battery?
The nominal capacity of sealed lead acid battery is calculated according to JIS C8702-1 Standard with using 20-hour discharge rate. For example, the capacity of WP5-12 battery is 5Ah, which means that when the battery is discharged with C20 rate, i.e., 0.25 amperes, the discharge time will be 20 hours.
What happens when a lead acid battery is discharged?
When the lead acid battery is discharging, the active materials of both the positive and negative plates are reacted with sulfuric acid to form lead sulfate. After discharge, the concentration of sulfuric acid in the electrolyte is decreased, and results in the increase of the internal resistance of the battery.
Personally, I always make sure that anything connected to a lead acid battery is properly fused. The common rule of thumb is that a lead acid battery should not be discharged below 50% of capacity, or ideally not beyond 70% of capacity. This is because lead acid batteries age / wear out faster if you deep discharge them.
It turns out that the usable capacity of a lead acid battery depends on the applied load. Therefore, the stated capacity is actually the capacity at a certain load that would deplete the battery in 20 hours. This is concept of the C-rate. 1C is the theoretical one hour discharge rate based on the capacity.
Is the capacity of a lead-acid battery a fixed quantity?
The capacity of a lead–acid battery is not a fixed quantity but varies according to how quickly it is discharged. The empirical relationship between discharge rate and capacity is known as Peukert's law.