Every calculation of backup battery starts from a figure that is actually the rarest for people to have: how many hours the system needs to last. The power of each device can be read on the label. The number of hours is usually guessed. However, that guess directly multiplies the cost, as battery capacity grows in proportion to the requested duration.
The number of hours is actually not a matter of preference. There is an official standard, and there is the realization, and the two are very different.
The official standard is one hour per month
Minister of Energy and Mineral Resources Regulation Number 27 of 2017, which has been amended by Minister of Energy and Mineral Resources Regulation Number 18 of 2019 and Minister of Energy and Mineral Resources Regulation Number 2 of 2025, regulates the Quality of Electricity Service. One of the indicators is the Duration of Outage, measured in hours per month per consumer.
Article 6A paragraph (1) establishes the amount for the Duration of Outage indicator at one hour per month. The Minister may set a different amount based on geographical conditions or existing network conditions. If the realization exceeds this amount, consumers are entitled to compensation, which is tiered according to how far the difference is:
| Difference above the standard | Compensation from the fixed charge or minimum bill |
|---|---|
| up to 2 hours | 50% |
| more than 2 to 4 hours | 75% |
| more than 4 to 8 hours | 100% |
| more than 8 to 16 hours | 200% |
| more than 16 to 40 hours | 300% |
| more than 40 hours | 500% |
This compensation is calculated on the electricity bill or the next month's token purchase, not paid separately.
The table above should be read as information for planning, not just consumer rights. The regulator itself has prepared a compensation class for outages exceeding 40 hours above the standard. This means that the rule makers consider that outages of that duration can occur. The battery measured for one hour is measured for the standard, not for its worst days.
The national realization is several times the standard
The commonly used indicator to see the big picture is SAIDI, the average duration of outages per customer per year. National Energy Council member Muhammad Kholid Syeirazi stated that the national average SAIDI rose from 5.34 hours per customer per year in 2024 to 8.48 hours in 2025, highlighting the realization of transmission network additions, which averaged only 42.3 percent of the RUPTL target over the past five years.
It should be noted that SAIDI is a national average. It mixes urban feeders that are rarely disturbed with end-of-line networks that are often disrupted. For purchasing decisions, the national average is too coarse.
The figures that truly belong to your location
Article 3 paragraph (1) requires PLN to announce the Quality of Service levels along with their realizations at each service unit, in a place easily accessible to consumers, at the beginning of each quarter. There, the Duration of Outage for the service unit covering your address can be seen. This is a basis that is much closer to reality than the national figures.
Outages that are not compensated are the ones that need to be anticipated
Article 7 exempts PLN from the obligation to compensate for the Duration of Outage indicator and the number of outages if the outages are necessary for maintenance, expansion, or rehabilitation of installations, if the outages are not due to PLN's negligence, if there are circumstances that potentially endanger public safety, or for investigative purposes. For maintenance work, consumers must be notified at least 24 hours in advance. Article 8 adds exceptions for force majeure causes such as floods, earthquakes, fires, and riots.
Note the pattern of exceptions. Scheduled outages and outages due to disasters are the two types most likely to last long, and both do not result in compensation. If batteries are purchased for peace of mind, those two scenarios are the real adversaries, not the one-hour outages that are already guaranteed by the standard.
Establishing two figures, not one
A more honest approach is to separate the two scenarios. First, short outages of a few hours with a reasonable load: lighting, routers, refrigerators, chargers. Second, long outages lasting a day with a much shorter list of devices. The second scenario often does not demand a larger battery, but rather requires a willingness to turn off more things.
Once the list of devices and the number of hours are established, the rest is just arithmetic, including deductions due to discharge limits and inverter losses. That part can be handed over to the backup battery size calculator.
Sources
- Minister of Energy and Mineral Resources Regulation Number 27 of 2017 on the Quality of Service and Costs Related to the Supply of Electricity by PT PLN (Persero), JDIH Ministry of Energy and Mineral Resources
- Minister of Energy and Mineral Resources Regulation Number 18 of 2019 on Amendments to Minister of Energy and Mineral Resources Regulation Number 27 of 2017, JDIH Ministry of Energy and Mineral Resources
- Minister of Energy and Mineral Resources Regulation Number 2 of 2025 on the Second Amendment to Minister of Energy and Mineral Resources Regulation Number 27 of 2017, JDIH Ministry of Energy and Mineral Resources
- Quality of Service Monitoring (TMP) is Becoming Tighter, Directorate General of Electricity, Ministry of Energy and Mineral Resources
- Ministry of Energy and Mineral Resources and DEN Request PLN to Improve the Reliability of the Sumatra Electricity System, Kontan, May 24, 2026