Portable Power Station House Backup: What It Really Runs

Two numbers on the label decide everything, a third one nobody reads decides whether the fridge starts, and how you connect it decides whether it is safe.

A portable power station is a battery, an inverter and a row of outlets in a
carrying case. It makes no fumes, so it can sit in a kitchen rather than in the
rain, and that single property is why so many New York households buy one after
a storm. What it will actually carry through the next one is a narrower question
than the packaging suggests, and it comes down to two numbers that are easy to
confuse.

Portable Power Station House Backup: What It Really Runs

Capacity is measured in watt-hours and answers how long. Output is
measured in watts and answers what can run at once. A large battery
behind a small inverter will keep a phone alive for days and refuse to start a
well pump at all; a large inverter on a small battery will start almost anything
and then empty in an hour. Both numbers have to be satisfied independently, and
a specification that leads with only one of them is telling you half the
story.

The third number nobody reads: surge

Anything with a motor — a refrigerator compressor, a sump pump, a well pump,
a furnace blower — draws several times its running wattage for the moment it
starts. A unit rated comfortably above an appliance’s running figure can still
fail to start it. The surge or peak figure on the specification is the one that
predicts this, and for motor loads it matters more than the continuous rating.

How you are allowed to connect it

This is the part that gets skipped, and it is the part with real
consequences. There are three arrangements, and only two of them are
legitimate.

• Extension cords to individual appliances. The honest
  default. Nothing to install, nothing to inspect, and it works for anything with
  a plug.
• A transfer switch or an interlock with an inlet. Permitted,
  inspected electrical work that lets the unit feed selected house circuits
  safely — which is the only way to reach hard-wired equipment such as a boiler,
  a furnace or a well pump. It is the same class of work as
  a generator inlet box install,
  and which circuits it serves is
  the subpanel question.
• Backfeeding through a dryer or range outlet with a
  double-ended cord. Never. It energises the house wiring with no
  disconnection from the utility, which puts voltage onto the service and onto
  lines that utility crews may be working on, and it leaves live pins exposed at
  one end of the cord. It is not a shortcut with a risk attached; it is the
  practice every transfer switch exists to prevent.

What it realistically carries in a New York outage

Recharging is the real difference from a fuel generator

A fuel generator runs as long as you can buy fuel. A portable battery holds
what it holds, and then the question is where the next charge comes from. Before
a forecast storm, the answer is the wall. During a multi-day outage it is a
vehicle, or portable solar panels, or nothing — and portable solar in a New York
December is a slow trickle rather than a refill.

So the honest way to think about a portable unit is as a fixed quantity of
energy you have stored, not as a supply. Work out what that quantity buys by
dividing capacity by the running draw of what you intend to keep alive, the same
arithmetic as
how long a home battery lasts in an outage.

Cold changes the number on the label

Battery capacity and, more sharply, the ability to accept a charge both fall
as temperature drops, and many units will refuse to charge below a threshold to
protect the cells. A power station stored in an unheated garage in February is
not the unit the specification describes. Keep it indoors and let it come up to
room temperature before relying on it — the same physics described in
cold weather and battery performance.

Where it sits against an installed system

An installed home battery is wired to selected circuits, switches over
automatically, is permitted and inspected, and is considerably larger. A
portable unit is manual, reaches only what you can plug into it unless a
transfer means is installed, holds far less, and can be carried to a different
house. Neither replaces the other, and the choice is mostly about whether you
want automatic coverage of specific circuits or a movable reserve — the
comparison in
a solar generator compared with a home battery,
and the scope decision in
whole-house backup or critical loads.

What to check on a specification sheet

• Capacity in watt-hours and continuous output in watts, as separate
  figures.
• The surge rating, if anything you care about has a motor.
• That the output is a pure sine wave, particularly for medical
  equipment.
• Cell chemistry and rated cycle life, since these differ substantially
  between units at similar prices.
• Pass-through operation, so it can sit charged and inline like a large
  uninterruptible supply.
• Charging inputs — wall, vehicle, solar — and the time each takes.
• Operating and charging temperature ranges, read against a New York
  winter.

Bought with those numbers in front of you, a portable unit is a genuinely
useful thing: it keeps food cold, keeps a household connected, and runs the
heating controls if the wiring was arranged in advance. Bought on the picture on
the box, it turns out to be a large phone charger during exactly the week it was
supposed to matter.

Frequently Asked Questions

Can a portable power station run a whole house?

No, and the marketing language around whole-house units is doing a lot of work. Two numbers limit it: capacity in watt-hours decides how long, and continuous output in watts decides what can run at once. Electric water heating, a range, a dryer, car charging and central cooling exceed both by a wide margin.

What is the difference between watt-hours and watts on the label?

Watt-hours are the size of the tank and watts are the size of the tap. A large battery behind a small inverter will run small things for a long time and refuse to start a pump; a large inverter on a small battery starts things easily and empties quickly. Both have to be adequate independently.

Why will it not start my refrigerator or pump?

Because motors draw several times their running wattage at the instant they start. The specification’s surge or peak figure predicts this, and a unit comfortably above an appliance’s running draw can still fail on startup. For motor loads the surge number matters more than the continuous rating.

Can I plug it into a dryer outlet to power the house?

No. Backfeeding through an outlet with a double-ended cord energises the house wiring with no disconnection from the utility, putting voltage onto the service and onto lines crews may be working on, and it leaves live pins exposed. Feeding house circuits legitimately requires a transfer switch or interlock with an inlet, which is permitted and inspected work.

How do I power my boiler or furnace with one?

Through a transfer means, because that equipment is hard-wired and has no plug. An interlock or transfer switch with an inlet lets the unit feed selected circuits safely, and it is the same class of installation as a generator inlet. Arrange it before the outage, not during one.

How do I recharge it during a long outage?

From a vehicle, from portable solar panels, or not at all. That is the real difference from a fuel generator, which runs as long as you can buy fuel. Portable solar in a New York winter is a slow trickle rather than a refill, so treat the unit as a fixed quantity of stored energy rather than a supply.

Does cold weather affect it?

Yes, in two ways. Usable capacity falls as temperature drops, and the ability to accept a charge falls more sharply, with many units refusing to charge below a threshold to protect the cells. A unit stored in an unheated garage in February is not the one the specification describes, so keep it indoors.