Contents
- What we checked ourselves: 102 hours on paper, about 29 in practice
- The short answer: five parts, one direction of flow
- What the BMS does while you are not looking
- Why the label math runs high
- Why small loads drain faster than the math says
- Inverter idle draw: the number the RIVER 2 Max page leaves out
- Formula versus reality, on three loads
- FAQ
- Sources
A portable power station is a battery pack with a few electronics wrapped around it. Cells store the energy, a battery management system (BMS) keeps them safe, and an inverter turns the stored DC into wall-style AC. The catch is that the inverter itself uses power just by being on, so paper runtime and real runtime drift apart.
We put a number on that. On a 512 Wh unit, a 5 W load runs 102 hours by the textbook formula and about 29 hours once inverter losses are counted. My view: if you only plan to run small loads, the idle draw matters more than the capacity figure.
What we checked ourselves: 102 hours on paper, about 29 in practice
Checked 2026-09-25 at 15:40. We took the 512 Wh capacity and 500 W rated AC output from the manufacturer’s product page for the EcoFlow RIVER 2 Max (opened 2026-09-25). Then we computed runtime two ways in a script.
- Naive: hours = Wh / load W
- Adjusted: hours = (Wh x usable fraction) / (load W / inverter efficiency + inverter idle W)
The usable fraction (0.90), the efficiency (0.85) and the idle draw (10 W and 15 W) are our assumptions. They are not values from that product page, which lists no inverter idle or efficiency figure. Plug in your own unit’s numbers to redo it.
| Load | Naive (Wh/W) | Adjusted, idle 10 W | % of naive | Adjusted, idle 15 W | % of naive |
|---|---|---|---|---|---|
| 5 W (router / LED strip) | 102.4 h | 29.0 h | 28% | 22.1 h | 22% |
| 10 W | 51.2 h | 21.2 h | 41% | 17.2 h | 34% |
| 60 W (laptop + monitor) | 8.5 h | 5.7 h | 67% | 5.4 h | 63% |
| 200 W | 2.6 h | 1.9 h | 73% | 1.8 h | 72% |
| 500 W (rated max) | 1.0 h | 0.77 h | 75% | 0.76 h | 75% |
Formula used: adjusted hours = (512 x 0.90) / (load / 0.85 + idle).
Read the caveats. These are assumptions, not measurements on a real unit. Real efficiency varies with load and is worse at very low load. Battery-side losses, temperature and battery age are ignored. And the DC and USB ports bypass the inverter and its idle draw, so small loads run much longer there.
At 500 W the same losses cost 25%. At 5 W they cost 72%. That gap is the whole story of this article.
The short answer: five parts, one direction of flow
Power moves through a fixed chain. Lithiumhub’s explainer lists five stages, in this order:
- Battery cells store the energy, usually LiFePO4.
- Charge controller manages incoming power when you charge, especially from solar. (Solar charging is its own topic. We skip it here.)
- BMS watches temperature, prevents overcharge and protects against short circuits.
- Inverter converts stored DC to AC. Lithiumhub notes that a pure sine wave output supports sensitive electronics.
- Output ports are AC outlets, USB, USB-C and DC connectors.
Two of those stages matter for runtime. The BMS runs all the time. The inverter runs whenever AC is on. Both take a cut before anything reaches your device.
Lithiumhub also sorts units by size: 100 to 500 Wh for light portable use, 500 to 1,500 Wh for emergency backup, and above 1,500 Wh for serious off-grid setups. That is a sense of scale, not a buying guide.
What the BMS does while you are not looking
The BMS is the part most people never think about. EcoFlow’s own explainer describes it as doing several jobs at once:
- Calculating how much charge is left
- Checking for internal shorts and poor contacts
- Keeping temperature in range
- Balancing charge between cells
- Cutting off when it detects a dangerous condition
EcoFlow also describes a Safe Operating Area: temperature, current and voltage limits the pack must stay inside. Outside it, thermal runaway becomes a risk. Charging below 0 °C (32 °F) is a problem too, because lithium plating damages the anode.
Why the label math runs high
The basic formula is simple: runtime in hours equals capacity in Wh divided by device power in W. It assumes every stored watt-hour reaches your device. It doesn’t. Some capacity is held back, the inverter loses energy converting DC to AC, and the inverter draws a flat amount of power just by being on. Our calculation above uses assumed values for the first two (0.90 and 0.85) and tests the third at 10 W and 15 W.
The efficiency factors are percentages. Idle is a flat number of watts. On a small load, a flat number hurts far more than a percentage does.
Why small loads drain faster than the math says
EDECOA writes the relationship plainly: total DC input equals the load plus the inverter’s standby draw. The idle draw is paid whether or not anything useful is plugged in.
How big is it? The sources disagree, probably because they describe different inverters. Portableenergylab puts idle with AC on and no load at typically 5 to 25 W. EDECOA gives 20 to 60 W for a mid-size inverter, and 5 to 10 W in a search (power-saving) mode. I would not force those into one range.
Portableenergylab gives three worked cases:
- Phone charging on a 500 Wh unit, idle 10 W. Two hours of charging uses 36 Wh. Eight hours of overnight idle uses 80 Wh. The idle costs more than the charging.
- Router on a 1,000 Wh unit, idle 10 W. On AC (25 W total) it lasts about 40 hours. On DC (15 W total) about 66 hours. Skipping the inverter buys roughly an extra day.
- 300 W device on a 1,500 Wh unit for 3 hours. Idle is about 3% of the energy used. On big loads, it barely registers.
EDECOA’s examples run the other way. A 40 W standby on a 2,000 Wh unit over 24 hours is 960 Wh, close to half the battery gone with nothing running. A 15 W router plus 35 W standby means 70% of the total draw is overhead. (We checked the arithmetic: 35 / 50 = 70%.)
The same logic covers any fixed overhead, such as a display or ports left switched on: it is a flat draw, so a low-wattage device pays proportionally more for it. We found no figure for a screen or for idle ports in the sources we read or on the product page, so we can’t put a number on it.
The fixes are cheap:
- Turn AC off when you are not using it.
- Batch your AC jobs together.
- Charge phones, tablets and small lights from the DC or USB ports.
- Track the state of charge over a fixed period to estimate your own unit’s idle draw.
Inverter idle draw: the number the RIVER 2 Max page leaves out
The EcoFlow RIVER 2 Max product page, opened on 2026-09-25, lists no idle or standby figure.
The numbers below come from owners and reviewers on forums and review sites, not from manufacturers. Treat them as a range, not a spec. We did not measure any of it.
Reports put AC idle draw at roughly 9 W to 40 W, depending on the model. Small units sit near the low end and large ones near the high end. Even two review sites disagree on the 1 kWh class (5-15 W versus 10-20 W). The range is here to show the spread, not to rank any brand.
The consequence is easy to compute. A 9 W idle alone empties a 512 Wh unit in about 57 hours (512 / 9 = 56.9) with nothing plugged in.
Formula versus reality, on three loads
The table at the top is illustrative and built on our assumed figures, so use it as a shape, not a promise. Three rows tell the story:
- 5 W router or LED strip: 102.4 h on paper, 29.0 h with idle at 10 W, 22.1 h at 15 W.
- 60 W laptop and monitor: 8.5 h on paper, 5.7 h or 5.4 h. That is 67% or 63% of the naive figure.
- 500 W at rated max: 1.0 h on paper, 0.77 h or 0.76 h. That is 75%.
Portableenergylab’s router example shows the same pattern. Its 1,000 Wh unit with 10 W idle gives about 40 hours on AC and about 66 on DC. The arithmetic checks out: 1,000 / 25 = 40 and 1,000 / 15 = 66.7. That version ignores efficiency and usable capacity, so it runs higher than ours would.
One caution. Every source above except our own calculation is a manufacturer or retailer blog. EcoFlow, EDECOA and Lithiumhub all sell or promote these products, and none of them is an independent test. That does not make the arithmetic wrong. It does mean the idle figures deserve a second look on your own unit.
My read: the industry’s favourite spec, capacity in Wh, tells you least about small loads. For a router or a light, check where it plugs in before you check the battery size.
FAQ
How does a portable power station work in one sentence? Cells store energy, a BMS protects them, and an inverter converts the DC to AC, with USB and DC ports available on the side.
Why does mine die sooner than Wh divided by watts says? Several losses stack up. Usable capacity and inverter efficiency are below 100%, and the BMS runs all the time. On small loads the inverter’s idle draw adds more. In our 512 Wh calculation, a 5 W load kept only 28% of the naive runtime, based on assumed figures.
How much power does the inverter use when nothing is plugged in? The RIVER 2 Max page we opened doesn’t list it. Reports from owners and reviewers put it at roughly 9 W to 40 W depending on the model, and those figures are second-hand.
Do USB and DC ports avoid the idle loss? They bypass the inverter and its idle draw. Portableenergylab’s router example shows about 66 hours on DC versus about 40 on AC.
Does cold weather matter? EcoFlow says charging below 0 °C (32 °F) can damage the anode through lithium plating.
Sources
- EcoFlow, Battery Management System Functions in Portable Power Stations
- Portableenergylab, Inverter Idle Consumption Explained
- Lithiumhub, What Is a Portable Power Station & How Does It Work?
- EDECOA, Inverter Standby Power
- Our own calculation and product-page checks, 2026-09-25
What is still open is the real idle draw of the unit on your shelf. The practical test is to leave AC on with nothing plugged in and watch the state of charge over a few hours. I’d like to see reviewers start measuring that gap between spec sheet and reality.
Image credits
- Photo by Compare Fibre on Unsplash