A discharge/charge cycle is commonly understood as the full discharge of a charged battery with subsequent recharge, but this is not always the case. Batteries are seldom fully discharged, and manufacturers often use the 80 percent depth-of-discharge (DoD) formula to rate a battery. This means that only 80 percent of the available energy is delivered and 20 percent remains in reserve. Cycling a battery at less than full discharge increases service life, and manufacturers argue that this is closer to a field representation than a full cycle because batteries are commonly recharged with some spare capacity left.
Related: Know about other types of Lead Acid batteries including Valve Regulated Lead Acid Battery (VRLA) i. AGM ii. GEL.
A crank battery has a large surface area with thin plates for quick surface chemical reactions and it is designed for cranking application and so the performance parameter is the cold cranking amperes a typical crank battery offers and not the backup. In contrast ‘deep discharge’ battery has thicker plates with a less exposed surface that forces the chemical reactions to move into the plates deeper during a discharge.
The main trade-off in battery development is between power and energy: batteries can be either high-power or high-energy, but not both.
Having said this, Tubular Lead Acid battery (OPzS) is undisputedly the most economical deep discharge battery and can be used for efficient backup.
There are some performance-related factors one should consider before choosing their battery:
- The Open-circuit Voltage (quiescent) at full charge
- The Open-circuit Voltage at full discharge
- Loaded Voltage at full discharge
- Equalization charging voltage
- Discharge rate curves (C1, C3, C5 and C10)
- Duty cycles for 20%, 35%, 50%, 80% DOD
- Self-discharge curve
A C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. A 1C rate means that the discharge current will discharge the entire battery in 1 hour. For a battery with a capacity of 100 Amp-hrs, this equates to a discharge current of 100 Amps. A 5C rate for this battery would be 500 Amps, and a C/2 rate would be 50 Amps. A 10C rate battery would be able to discharge 1000 Amps without doing damage to the battery.
There are some very critical certification-related aspects that need to be checked:
- IEC Standard PV solution compliance 60896 (TC 21/TC 82)
- IEC Standard compliance 60896-11
- IEC Standard compliance 60896-2
- IEC Standard Cycling test 61427
- IEC 61147/ NF C58-510
- IEEE 535 Lead Selenium aging result for Tubular Batteries
The purpose of a battery is to store energy and release it at the desired time. Properly manufactured stationary batteries of tubular design are an excellent candidate for long-duration duty cycles of two (2) to one-hundred (100) hours of standby application as well as cyclical requirements.
Duty Cycle: The complete charge and discharge of a battery at a certain DOD constitute one complete duty cycle.
Note: In Pakistan, effectively the battery undergoes an average of 2 duty cycles a day, and therefore at a certain DOD, we can calculate the life expectancy in years of a battery by dividing the claimed duty cycles divided (by 2*365 days).
Depth of Discharge (DOD): Is the useful percentage window of discharge available between floating voltage and loaded voltage at discharge.
Note: 100 Ah battery with nominal 10-hour discharge rate (C10) can ideally allow a drain of 20A in 1 hr at 20 percent DOD at 10-hour discharge rate.