Methodology: how every number is calculated
Every number on this site comes from the formulas below, applied to sourced specs. Where a maker publishes nothing, a documented assumption fills in, and the page that uses it says so.
Questions or corrections
hello@kilohour.comKey defaults
- Usable share of rated capacity
- 90%
- Inverter efficiency
- 88%
- Inverter idle draw (W)
- 10 W
- Solar harvest vs panel rating
- 75%
- Runtimes
- Rounded down, never up
Runtime on the AC outlets
Usable energy is the rated capacity times the usable share times battery health. The battery then has to cover the appliance's average draw, raised by inverter losses, plus the inverter's own idle draw:
usable Wh=rated Wh×usable share
hours=usable Wh÷(load W÷inverter efficiency+idle W)
- Manufacturer spec, linked to its source
- Assumption when the maker publishes nothing, always labeled
- Your appliance and how you use it
The average draw is the running watts times the duty cycle, the share of time the appliance actually draws power (a fridge compressor cycling on and off).
Runtime on a DC port
On a 12 V car port or USB-C, the battery draw is the DC load ÷ DC efficiency + DC idle draw, which skips the inverter. The device's DC draw must fit the port's rating; above 90% of the rating the site warns that the port may trip when the device starts, which is common with CPAP DC converters on 120 W car ports.
Cautious, typical and optimistic
Each answer is a range. The cautious runtime moves efficiency by -5 points and raises idle draw by 50%. The optimistic runtime moves efficiency by +3 points, capped at 98%. Runtimes round down to the minute, and nights and days round down to one decimal, so a number here is never more than the math supports.
Can it run? The verdict
| Verdict | When |
|---|---|
| Can't run it | The running watts exceed the continuous rating, or the biggest motor starting while the rest run exceeds the surge rating. |
| Runs briefly | It runs, but for less than an hour (a space heater, for example). |
| Tight fit | The load is above 80% of the continuous rating, the startup peak is above 90% of the surge rating, or the runtime is shorter than the hours you need. |
| Runs it | Every margin holds. |
Boost modes (X-Boost, SurgePad, Power Lifting) raise the limit only when every load is a pure resistive heater and the load is above the continuous rating, because those modes run resistive loads at reduced power.
Outages, trips and solar
The planner adds up each appliance's daily energy (watts × duty cycle × hours a day × quantity), divides AC loads by inverter efficiency and DC loads by DC efficiency, and adds the inverter's idle draw for the hours it is on. Solar adds min(panel watts, the station's solar input limit) × peak sun hours × 75% a day. Days supported are usable energy divided by what solar leaves uncovered; if solar covers the whole day, the setup is sustainable.
Solar recharge time is the energy to refill divided by the clipped panel watts × the derate, given in hours of full sun and in days at a chosen number of peak sun hours.
Every assumption
These defaults apply only when a station or appliance publishes nothing better.
| Assumption | Default | Why |
|---|---|---|
| Usable share of rated capacity | 90% | Makers stop short of a full discharge to protect the pack. BLUETTI puts depth of discharge for its LiFePO4 packs at 90% to 95% and uses 90% in its runtime formulas. Used when a station publishes nothing; adjustable. Source: bluettipower.com |
| Inverter efficiency | 88% | Converting battery power to 120 V AC loses energy as heat, more at light loads. BLUETTI calls 85% or better the standard for portable stations and quotes 90% to 93% for its best units; Anker measured an industry average of 76% at a 100 W load. 0.88 is a moderate-load figure; adjustable from 0.80 to 0.92. Source: bluettipower.com |
| Inverter idle draw (W) | 10 W | With the AC outputs on and nothing plugged in, the inverter still draws power. Anker lists 10 W for its S2000 against an industry average of 17 W for mainstream 2 kWh stations, so 10 W is the low end. The cautious estimate raises it by half; adjustable. Source: ankersolix.com |
| DC output efficiency | 95% | Regulated 12 V and USB-C outputs use DC-DC converters. A Texas Instruments USB-C PD reference design measures about 93% to 97% at moderate load, less at light load and at 5 V. Source: ti.com |
| DC idle draw (W) | 2 W | No maker publishes the idle draw with only the DC outputs on. 2 W covers the display and DC output stage; a judgment, not a measured figure. No published source; a stated judgment. |
| Battery health | 100% | Assumes a new battery. Packs lose capacity with age and cycles, so it can be lowered for an older unit; no fixed aging curve is claimed. No published source; a stated judgment. |
| Continuous headroom | 80% | The US electrical code sizes a circuit at 125% of a continuous load (one running three hours or more), which caps that load at 80% of the rating. The same headroom applies to the inverter: loads above 80% of its continuous rating are flagged as tight. Source: resources.kohler.com |
| Surge headroom | 90% | Motors and compressors can start at 2 to 4 times their running watts, and that inrush varies between units, so a startup peak within 10% of the rated surge is flagged as tight. Source: s4.bluettipower.com |
| Solar harvest vs panel rating | 75% | NREL's PVWatts assumes 14% system losses (soiling, shading, wiring, mismatch and more) and counts heat losses on top of that. Portable panels also lose energy to imperfect angles and the charge controller, so 75% of the panel rating is a conservative planning figure. Source: pvwatts.nlr.gov |
| Peak sun hours per day | 3 / 4.5 / 6 h | One sun-hour is 1 kWh of sunlight per square meter. An NREL presentation puts the daily total at 3 to 6 over most of the continental US, and about 4.5 for Colorado. Source: energy.gov |
Where specs come from
Station and appliance values come from manufacturer product pages, spec sheets and user manuals, and from ENERGY STAR and US government data for generic appliances. Every value links to its source and shows the date it was last checked. A value nobody publishes stays empty instead of being guessed, and rows not re-checked within 180 days are flagged for review.
Medical devices
Estimates only, not medical advice. Power needs vary by device, pressure, humidifier and tubing settings. Always have a backup plan for medical devices and follow your device manufacturer's power guidance. Consult your equipment provider before relying on battery power.