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Discharge efficiency Self-discharge rate Shelf life ... Low self-discharge nickel–metal hydride battery: ... 85–90 6,000–30,000 to 90% capacity
Manufacturers specify the capacity of a battery at a specified discharge rate. For example, a battery might be rated at 100 A·h when discharged at a rate that will fully discharge the battery in 20 hours (at 5 amperes for this example). If discharged at a faster rate the delivered capacity is less.
The Headway 38120HP cells are used in high-discharge environments as they have very good continuous/peak discharge rates (10C/25C). Because four cells in series produces a voltage range similar to 6 cells of lead-acids and their fire-resistant properties, they can be used to replace a 12 V lead-acid car battery. [235] 38140: 38140s 12,000 38: 140
An AA-sized alkaline battery might have an effective capacity of 3000 mAh at low drain, but at a load of 1 ampere, which is common for digital cameras, the capacity could be as little as 700 mAh. [12] The voltage of the battery declines steadily during use, so the total usable capacity depends on the cutoff voltage of the application.
The relationship between the Ah capacity and the discharge rate is not linear; as the discharge rate is increased, the capacity decreases. A battery with a 100 Ah rating generally will not be able to maintain a voltage above 10.5 volts for 10 hours while being discharged at constant rate of 10 amps. Capacity also decreases with temperature.
The higher the discharge rate, the lower the capacity. [50] The relationship between current, discharge time and capacity for a lead acid battery is approximated (over a typical range of current values) by Peukert's law: = where is the capacity when discharged at a rate of 1 amp.
The developers claim a large increase in recharge cycles to around 40,000 and higher charge and discharge rates, at least 5 C charge rate. Sustained 60 C discharge and 1000 C peak discharge rate and a significant increase in specific energy, and energy density. [43] lithium iron phosphate batteries are used in some applications.
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.