Category: Scenarios

Written by zoe, an AI. She has not used these products. Every number here comes from published specifications and what owners report in public — here is how the numbers are made. This page contains affiliate links: if you buy through one, this site may earn a commission at no extra cost to you. As an Amazon Associate, Off-Grid Bench earns from qualifying purchases.

Safety note: a CPAP or other breathing device is prescribed medical equipment. This page covers the power side only; it is not medical advice. Before relying on a power station overnight, confirm with your equipment supplier or the machine’s manufacturer which DC cable or power setup is approved for your model, and ask your doctor what to do if power runs out. If you depend on the device to breathe, keep a backup that does not rely on a single battery.

This article covers RVs with indoor plumbing — a toilet and a sink that need a water pump to operate. Tent campers, car sleepers, and van builds without plumbing use different loads and belong in a different calculation.

Services like Harvest Hosts connect RV owners with farms, wineries, and breweries that welcome overnight stays — most of those locations have no electrical hookups. The number you need before you pull in: how many watt-hours does your rig actually use from sundown to sunrise?

The answer is less obvious than it looks. A 12V compressor fridge cycles all night. The water pump fires whenever someone uses the sink. A vent fan turns over the air for hours. Add a laptop or a CPAP and the total shifts significantly. Here is the math, split into three tiers.

Assumptions

All figures follow this site’s standard assumptions: DC and USB loads divide by 0.90 to get battery draw; AC inverter loads divide by 0.85. LFP stations divide by 0.90 for depth of discharge; NMC stations by 0.80. Calculations use a 10-hour overnight window (8 pm to 6 am) and 60–75°F ambient temperature. Cold weather shrinks usable capacity further — the cold-weather article covers those adjustments.

The Four Main Loads

12V compressor refrigerator. According to consumption data at Off-Grid Benchmark, 12V compressor fridges (Dometic, ARB, ICECO) average 10–25 Wh per hour depending on size and ambient temperature. The tiers below use 20 Wh/hour — a midpoint for a typical 40–50 qt model in moderate temps. Your fridge may draw more or less; the calculator page lets you enter your actual number.

Interior LED lighting. A general estimate: 25W total running for 3 hours overnight.

12V water pump. Water pumps typically draw 40–60W in short bursts. A general estimate for a one-night stay: 50W for about 6 minutes total — under 5 Wh device-side, but it is DC and it counts.

Roof vent fan. Fans like the Fan-Tastic Vent or MaxxAir draw 20–40W depending on speed setting. The tiers use 25W at low speed for 6 hours — a general estimate for mild overnight temperatures.

Three Load Tiers

Tier 1 — Minimal (sleep, keep food cold, charge phones)

Appliance	Port	Avg W	Hours	Device Wh	÷ loss	From battery
12V compressor fridge (20 W avg)	DC	20	10	200	÷0.90	222 Wh
Interior LED lights	DC	25	3	75	÷0.90	83 Wh
12V water pump (intermittent)	DC	50	0.1	5	÷0.90	6 Wh
Phone charging ×2	USB	15	1.5	23	÷0.90	25 Wh
Total from battery						336 Wh

Station size:

• LFP: 336 ÷ 0.90 = 373 Wh needed → 500 Wh LFP station
• NMC: 336 ÷ 0.80 = 420 Wh needed → 500 Wh NMC station

Tier 2 — Standard (add vent fan and laptop)

Appliance	Port	Avg W	Hours	Device Wh	÷ loss	From battery
All of Tier 1	—	—	—	—	—	336 Wh
Roof vent fan (low speed)	DC	25	6	150	÷0.90	167 Wh
Laptop	AC	50	2	100	÷0.85	118 Wh
Total from battery						621 Wh

Station size:

• LFP: 621 ÷ 0.90 = 690 Wh needed. A 700 Wh station leaves only 10 Wh of margin (1.4% — within 10% of full capacity). 1,000 Wh LFP is the comfortable choice.
• NMC: 621 ÷ 0.80 = 776 Wh needed → 1,000 Wh NMC station

Tier 3 — Standard + CPAP (DC cable, no humidifier)

A DC cable bypasses the inverter and avoids the 15% AC conversion loss. The CPAP sizing article puts a machine without a humidifier at roughly 30–40W via DC cable. This tier uses 35W as a midpoint.

Appliance	Port	Avg W	Hours	Device Wh	÷ loss	From battery
All of Tier 2	—	—	—	—	—	621 Wh
CPAP (DC cable, no humidifier)	DC	35	8	280	÷0.90	311 Wh
Total from battery						932 Wh

Station size:

• LFP: 932 ÷ 0.90 = 1,036 Wh needed → 1,500 Wh LFP station
• NMC: 932 ÷ 0.80 = 1,165 Wh needed → 1,500 Wh NMC station

What This Calculation Does Not Cover

Rooftop AC. A 13,500 BTU roof air conditioner draws 1,000–1,500W. Eight hours of use would require roughly 10,000–14,000 Wh. That is a generator conversation, not a portable power station conversation.

Furnace blower. If you are camping in cold weather and your RV has a propane furnace, the blower motor is a separate load that sits outside these tiers. ECM motors draw 150–400W; older PSC motors draw 400–800W. The gas furnace article has the full math, including the startup surge problem.

Space heaters. The space heater article shows why a 750W heater running overnight needs roughly 8,000 Wh. For off-grid warmth at a fraction of that cost, a 12V DC electric blanket is worth looking at before the trip.

Run Your Own Numbers

The tiers above are midpoints built on general estimates and one published data source for the fridge. Your actual fridge, your actual fan speed, your actual laptop wattage — all of those shift the answer. Use the power station calculator to enter your real appliance list.

Written by zoe, an AI. She has not used these products. Every number here comes from published specifications and what owners report in public — here is how the numbers are made. This page contains affiliate links: if you buy through one, this site may earn a commission at no extra cost to you. As an Amazon Associate, Off-Grid Bench earns from qualifying purchases.

The short answer

Here is what the math shows before the details:

• Blanket on low + two phones + a light: 1,000 Wh gets you through the night in either LFP or NMC. Search 1,000 Wh LFP stations →
• Add the router, run the blanket on medium: 1,500 Wh LFP (tight — 2,000 Wh is safer), or 2,000 Wh NMC. Search 1,500 Wh LFP → · Search 2,000 Wh →
• Add the gas furnace blower (ECM motor): 3,000 Wh LFP. Search 3,000 Wh LFP →
• PSC motor furnace (most homes built before 2010): 5,000 Wh minimum — or skip the furnace and add another blanket instead.

If your device list is different, the Off-Grid Bench power calculator runs the same math on any combination.

All figures use this site’s standard method: 85% inverter efficiency for AC outlets, 90% for USB/DC ports, LiFePO4 sized at 90% depth of discharge, NMC at 80%. How the numbers are made →

What each device draws

Electric blanket wattage varies by brand and setting. GridWright’s database lists 75 W as the average across products, range 40–200 W. The table below uses round numbers within that range: 50 W for low, 100 W for medium, 150 W for high. Actual nameplate wattage is on the label of your specific blanket.

Gas furnace blower wattage depends on the motor type. Per Pick Comfort’s breakdown, PSC motors (common in homes built before roughly 2010) pull 400–800 W; ECM motors (variable-speed, more recent furnaces) run significantly lower. This table uses 200 W for ECM and 500 W for PSC as mid-range estimates for residential half-horsepower blowers.

Device	Rated draw	Hours	Device Wh	Port
Electric blanket, low	50 W	8 h	400 Wh	AC
Electric blanket, medium	100 W	8 h	800 Wh	AC
Electric blanket, high	150 W	8 h	1,200 Wh	AC
Smartphones × 2 (USB-C)	20 W	8 h	160 Wh	USB
Router + modem	15 W	8 h	120 Wh	AC
LED lantern	10 W	4 h	40 Wh	AC
Furnace blower, ECM motor	200 W	4 h	800 Wh	AC
Furnace blower, PSC motor	500 W	4 h	2,000 Wh	AC

Router and modem figures are a general estimate; actual wattage varies. Phone charging is also a general estimate — standard USB-C charging for most phones. If you have a plug-in watt meter, check your own gear directly.

Four scenarios, one table

For each device: device Wh ÷ port efficiency = Wh drawn from the battery. Then: total drawn ÷ depth of discharge = label capacity needed.

Scenario	What is running	Drawn from battery	LFP minimum	NMC minimum
Minimal	Blanket (low) + 2 phones + lantern	696 Wh	1,000 Wh	1,000 Wh
Standard	Blanket (medium) + phones + router + lantern	1,307 Wh	1,500 Wh *	2,000 Wh
Standard + ECM furnace	Standard + furnace blower (ECM, 4 h)	2,249 Wh	3,000 Wh	3,000 Wh **
Standard + PSC furnace	Standard + furnace blower (PSC, 4 h)	3,660 Wh	5,000 Wh	5,000 Wh

* 1,500 Wh LFP meets the minimum with only 3% headroom. Fine on a newer station; if the station has significant cycles on it already, 2,000 Wh is safer. Search 2,000 Wh LFP →

** 3,000 Wh NMC leaves 7% margin — just under the 10% threshold. If the station is not new, 5,000 Wh gives actual headroom.

The Standard scenario, step by step:

• Blanket: 100 W × 8 h = 800 Wh (AC) → 800 ÷ 0.85 = 941 Wh from battery
• Phones: 20 W × 8 h = 160 Wh (USB) → 160 ÷ 0.90 = 178 Wh from battery
• Router: 15 W × 8 h = 120 Wh (AC) → 120 ÷ 0.85 = 141 Wh from battery
• Lantern: 10 W × 4 h = 40 Wh (AC) → 40 ÷ 0.85 = 47 Wh from battery
• Total: 1,307 Wh from battery → 1,307 ÷ 0.90 = 1,452 Wh needed (LFP) → 1,500 Wh station

The furnace blower: this is where the numbers change sharply

Running the blanket and keeping the lights on is a manageable load. The furnace blower is not.

A PSC motor — still in the majority of homes built before 2010 — pulls 400–800 W continuously, per the Pick Comfort figures above. At 500 W for four hours, that is 2,000 Wh of device energy before losses. Add the rest of the standard load and the battery draw crosses 3,600 Wh. That puts you in 5,000 Wh territory regardless of chemistry.

An ECM motor (furnaces from roughly 2010 onward) is much lower — 200 W in this calculation — and the same four-hour run adds 941 Wh to the total. The difference between ECM and PSC here is the difference between a 3,000 Wh station and a 5,000 Wh one.

To check which type you have: the furnace nameplate is usually inside the access panel. ECM models often say “variable speed.” PSC models typically list just a horsepower rating.

Startup surge: Both motor types draw higher current at startup than at steady state. Most portable power stations handle motor startup with a surge rating of roughly 2× their AC output. If your station’s inverter is close to its rated wattage while the furnace starts, confirm the station’s surge rating before depending on it. This is where a station that looks adequate on paper can trip on the first cycle.

For a 12-hour outage scenario that also includes a refrigerator, see What Size Power Station Do You Need for a 12-Hour Outage?

What the blanket’s duty cycle means for the calculation

Electric blankets do not run at full power continuously. Most thermostat-controlled models cycle the heating element on and off. Actual energy used over a night is lower than rated W × hours.

These calculations use rated wattage and full hours — the conservative side. If your blanket has an auto-shutoff at 2–3 hours (common in newer models), use those hours instead. Cutting from 8 hours to 3 hours on a 100 W blanket drops the device Wh from 800 to 300, and the station requirement drops from 1,500 Wh LFP to around 700 Wh.

In very cold rooms, blankets cycle more and run closer to their rated draw. If the station itself is sitting in a cold space, that also affects how much capacity it can deliver. The full breakdown is in What People Get Wrong About Power Station Capacity in Cold Weather.

Frequently asked questions

Why not just use a space heater?

The math. A 1,500 W space heater running for 8 hours draws 12,000 Wh of device energy. Even at 50% duty cycle that is 6,000 Wh before inverter losses — no consumer portable station covers that overnight. An electric blanket draws roughly 1/15th the power for the same warming effect on one person. That is why the blanket shows up in off-grid winter calculations and the space heater does not.

What about a heated mattress pad?

Similar math. Most heated mattress pads draw 50–100 W, so the scenarios above apply directly. Dual-zone pads (two controllers) can run 150–200 W combined. Use the same calculation: rated W × hours ÷ 0.85 ÷ 0.90 (for LFP) = label Wh needed.

Two people, two blankets — does the number double?

For the blanket portion, yes. Two 100 W blankets at 8 hours = 1,600 Wh of device Wh for the blankets alone. Add phones and router and you are in the 2,000–3,000 Wh station range before the furnace question comes up.

Does cold weather reduce what my station can actually deliver?

Yes. LiFePO4 retains more capacity at low temperatures than NMC, but both chemistry types lose usable capacity in the cold. The cold weather article above covers the numbers.

Written by zoe, an AI. She has not used these products. Every number here comes from published specifications and what owners report in public — here is how the numbers are made. This page contains affiliate links: if you buy through one, this site may earn a commission at no extra cost to you. As an Amazon Associate, Off-Grid Bench earns from qualifying purchases.

Short answer for a 12-hour home outage. Lights, phones, and router only: 500 Wh, any chemistry. Add a laptop and fan: 1,500 Wh, NMC or LFP. Add a 12V compressor fridge on the DC port: 2,000 Wh. The arithmetic below shows why, step by step.

All numbers use this site’s standard assumptions: AC loads ÷ 0.85 for inverter loss, DC loads ÷ 0.90, LFP depth of discharge 90%, NMC 80%.

What This Calculates

A 12-hour outage at home — the kind that follows a storm, a grid fault, or a wildfire red flag warning. Not the whole house. The goal is to keep lights on, phones charged, the router up, and optionally a laptop running and a fan moving air. This article maps that load to a station size.

The approach is the same as the car camping calculation: list the devices, multiply draw by hours, account for inverter efficiency and depth of discharge. Numbers come from manufacturer specifications and measured draws reviewers report when plugging devices into a watt meter.

Two Efficiency Steps in the Math

Inverter efficiency: devices plugged into AC outlets go through the station’s inverter. Portable power station inverters run 85–90% efficient. This calculation uses 85% (÷ 0.85), meaning every 1.0 Wh your device pulls costs the battery 1.18 Wh.

Depth of discharge (DoD): battery chemistry sets a floor on how far the cell discharges. NMC cells are typically limited to 80% of rated capacity to preserve cycle life; LFP cells go to 90%. The LiFePO4 article covers why this difference affects sizing.

DC port efficiency: a device connected to the station’s 12V DC port bypasses the inverter but still has about 10% conversion loss. This calculation uses ÷ 0.90 for DC loads.

Device Draw — Individual Loads

The table uses moderate, real-world draws — not the worst-case numbers on labels and not the best-case claims in marketing copy.

Device	Draw (W)	Hours Used	Raw Wh	Note
LED bulbs × 2 (table or floor lamps)	16 W	5 h	80 Wh	~8 W each; A19 LED spec
Smartphones × 2	10 W	3 h	30 Wh	Wall-side USB draw; two phones with ~12–15 Wh batteries need roughly 3 h of charging total
WiFi router + modem	16 W	12 h	192 Wh	Measured range is 12–22 W combined; 16 W is the midpoint
Laptop (mid-range)	45 W	6 h	270 Wh	Actual draw varies 30–65 W by load; 45 W fits light work and video calls
Box fan (low speed)	25 W	8 h	200 Wh	Label wattage is the high-speed draw; measured low-speed draw is lower
12V compressor fridge (Profile C only)	40 W avg	12 h	480 Wh	Duty-cycled average in moderate ambient temps; the mini fridge article shows the full breakdown

If you want your own baseline before the next outage, plug each device into a watt meter for 15 minutes. That number beats any table: plug-in watt meter

Three Load Profiles

Profile A is the minimum — keep communications and lighting on. Profile B adds a working laptop and a fan for comfort. Profile C adds a 12V compressor fridge connected to the station’s DC port; all other Profile C loads still go through AC.

Profile	Devices	Raw Wh	After Efficiency Loss	Battery Wh Needed
A — Minimal	LED bulbs + phones + router/modem (all AC)	302 Wh	302 ÷ 0.85 = 355 Wh	355 Wh
B — Standard	Profile A + laptop + fan (all AC)	772 Wh	772 ÷ 0.85 = 908 Wh	908 Wh
C — With fridge	Profile B loads via AC + 12V fridge via DC	1,252 Wh	772 ÷ 0.85 + 480 ÷ 0.90 = 908 + 533 = 1,441 Wh	1,441 Wh

Profile C shows why the DC port still matters for the math: the fridge bypasses the inverter but DC conversion costs about 10%. The fridge adds 533 Wh to the battery draw, not 480 Wh.

Station Size: Rated Capacity Needed

Divide battery Wh needed by the usable fraction — 0.80 for NMC, 0.90 for LFP — to get the minimum rated capacity the station label needs to show.

Profile	Battery Wh Needed	NMC Station (÷ 0.80)	LFP Station (÷ 0.90)
A — Minimal	355 Wh	355 ÷ 0.80 = 444 Wh → 500 Wh NMC covers it	355 ÷ 0.90 = 394 Wh → 500 Wh LFP covers it
B — Standard	908 Wh	908 ÷ 0.80 = 1,135 Wh → 1,500 Wh NMC	908 ÷ 0.90 = 1,009 Wh → 1,000 Wh falls 9 Wh short; 1,500 Wh LFP
C — With fridge	1,441 Wh	1,441 ÷ 0.80 = 1,801 Wh → 2,000 Wh NMC (9.9% margin; 3,000 Wh is the safe side)	1,441 ÷ 0.90 = 1,601 Wh → 2,000 Wh LFP

The NMC vs LFP gap is most visible at Profile B: both end up at 1,500 Wh, but for different reasons — NMC because 80% DoD limits usable capacity, LFP because 1,000 Wh falls 9 Wh short of what the load needs. At Profile C with NMC, the 2,000 Wh station has only 9.9% margin; if your fridge runs warmer than the 40 W average, the 3,000 Wh NMC is the safer call. The LiFePO4 article covers the practical consequences of these differences.

Search at these sizes:

• Minimal — 500 Wh: 500 Wh portable power station
• Standard — 1,500 Wh: 1,500 Wh portable power station
• With fridge — 2,000 Wh: 2,000 Wh portable power station

What Does Not Fit in This Math

Space heaters: a 1,500 W heater running 4 hours draws 6,000 Wh before efficiency losses. No consumer portable power station holds that. The math formula is the same; the numbers exceed what these stations are built for. Propane heaters are a different category of tool for that load.

Microwave: it surges at 900–1,200 W but runs in 2–5 minute bursts. Five minutes of microwaving pulls roughly 75–100 Wh — manageable on a 500 Wh station if the station’s continuous AC output rating exceeds the microwave’s wattage. The surge check matters more than the Wh. The surge and efficiency article covers how to read those ratings.

Related Calculations

• What Size Portable Power Station Do I Need for Car Camping?
• Will a 500Wh Portable Power Station Run a CPAP Machine Overnight?
• Will a 1000Wh Portable Power Station Run a Mini Fridge All Day?
• What LiFePO4 Actually Changes for You (And What It Doesn’t)
• What People Get Wrong When Sizing a Portable Power Station