Load Shedding and Battery life
According to the Manufacturers specifications, a CSB battery has approx. 260 life cycles at 100 % discharge to 11.8 V
The way Manufacturers calculate this is that they expect under stable grid conditions, their batteries should experience one discharge per week, which would equate to a lifespan of approximately 5 years. (assuming perfect temperature, charging etc)
This minimum weekly interval between discharges, allows the battery banks to fully recharge before the next discharge occurs.
Introduce Load Shedding @ 100% discharge
During Stage 2 load shedding, over 1 week there are about 10 outages which means 10 battery discharges per week. Most of the time the batteries or battery bank has not fully recharged before being discharged again (please see charging times below) and this will result in a reduced expected runtime and damage to the battery.
So, if we have 2 weeks of Stage 2 load shedding, 5-6 months of the battery’s expected lifetime (5 years) have been “used up” in just those two weeks. Bear in mind too that the batteries would not have been fully charged to 100% thereby depleting the life cycle further.
From these facts, we can safely assume that 2 weeks of Stage 2 load shedding with insufficient breaks between outages to allow full recharging of batteries will “use up” approx. 8 months worth of the battery’s life expectancy and will degrade the battery capacity.
Stage 4 has 50% more outages than Stage 2 so the equation just gets worse.
Important to note another factor is that most UPS will only cut off when the battery is discharged to 10.5 V ( 200 % discharge ) which will further degrade the battery.
BATTERY CHARGE TIMES to Full charge wich is 12.8V
12.5V @ 30% discharge – 8 Hours to charge to 100%
12.3V @ 30 % to 50% discharge – 12 hours to charge to 100 %
11.8V @ 50 % to 100 % discharge – up to 24 hours to charge to 100 %
‘Before any NEW battery is used it needs to be fully recharged for 24 hours’
If you are installing a new battery during a period of load shedding and a full charge does not occur, this can impact the capacity of the battery over its lifespan.
Current Load Shedding Statistics
- 2019 had a duration of 530 hours of load shedding ,which equates to 265 x 2 hour load shedding,
- 2020 has already surpassed this quantity as of 2nd September (Source, CSIR).
Bearing in mind that an average battery has approximately 250 full discharge cycles under ideal conditions, in 2019 your standby battery would have fully exhausted the manufacturer’s estimated lifespan within that year.
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