What battery duration means, why the NEM is shifting from 1- and 2-hour to 4-hour systems, and how duration shapes revenue per MW versus revenue per MWh.
A battery's duration is how many hours it can sustain full output — its energy capacity (MWh) divided by its power capacity (MW). A 100 MW / 200 MWh system is a 2-hour battery; a 100 MW / 400 MWh system is a 4-hour battery. Duration is one of the most important things about a battery's economics, and it is quietly shifting across the NEM fleet.
A short-duration battery (1–2 hours) can throw its full power at the market, but only briefly — it empties before a long evening peak is over. A long-duration battery (4 hours or more) holds less power relative to its stored energy, but can keep discharging right across an extended high-price window, and can shift larger volumes of cheap midday energy into the peak. As solar deepens the daily price shape, the high-price window widens, and the value of being able to run through all of it rises. That is why new NEM investment is tilting toward 4-hour systems, and increasingly beyond.
Duration also decides which yardstick flatters a battery. Revenue per MW (power) tends to favour short-duration units, because they concentrate all their capacity into the few highest-value intervals. Revenue per MWh (energy) tends to favour long-duration units, because it rewards spreading stored energy across the day. Neither is "right" — they answer different questions, and looking at both is the only way to tell whether a unit is doing well because of good dispatch or simply because of favourable sizing.
Duration matters most for energy arbitrage. A battery earning primarily from FCAS needs power headroom and enough charge to sustain a response, but does not need to run for hours at full tilt, so short-duration units can still do well where FCAS is the main game. This is part of why the NEM's early batteries — built when FCAS was the richer market — skewed short, and why the shift to longer duration tracks the shift toward energy arbitrage as the fleet grows.
Every battery page on NEMPulse states the unit's duration and duration class, so you can see at a glance which end of this spectrum it sits on before reading its revenue.
More guides: Why do battery revenues rise and fall in the NEM?How does a grid-scale battery make money in the NEM?
See also: Revenue per MW — glossaryRevenue per MWh — glossaryBattery fleet
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