How Many Watt Hours Do You Actually Need

You are standing in a shop aisle, or scrolling a product page, and every power station shows a different watt hour number. Which one covers your weekend, your fridge or your work day? This page walks you through the sums, step by step, so you can pick a battery size from your own loads rather than from a guess.

Step 1: List every device you want to run

Start with a plain list. Write down each thing you would plug in: phone, laptop, lights, a fridge, a CPAP, a fan. Leave out anything you could do without. The list is the foundation of the whole sum, and a short, honest one beats a long, hopeful one. Small lists suit the smallest stations, which are easy to carry and cheap to charge.

Step 2: Find the real wattage and the run time

Look for the wattage on the device label or power brick. Then estimate hours of use. Some devices do not draw their label wattage all the time. A fridge cycles on and off, so its average is lower than its rating. A laptop charger draws more when the battery is low. Multiply watts by hours to get watt hours for each item, then add the column up. Also note the biggest single draw, because the inverter has to handle that at once. Ratings such as 600W or 700W are the ceiling for what you run together.

Step 3: Add inverter losses

A power station stores energy as DC and converts it to AC for your plugs. That conversion costs some energy. A common rule of thumb is to add around 15 to 20 per cent to your total. Using DC or USB ports directly can skip some of that loss. Then add a little spare so you are not draining the battery to zero. So if your list adds up to 500Wh, aim for roughly 600 to 650Wh or more. Stations in the 700 to 900Wh range fit that sort of target.

Example 1: A weekend camp

Say two nights. Phones and a camera charge for about 100Wh in total, LED lights use about 60Wh, and a small fan uses about 120Wh over the two nights. That is around 280Wh. Add losses and you land near 330Wh. A mid-size unit gives you room, and if you can bring a solar panel, you can top up by day. The EB3A lists solar plus AC dual charging, and the AC70P and AC70 sit comfortably above this load.

Example 2: A fridge during an outage

A modern fridge may average somewhere around 1 to 2kWh a day, though your own label and use will differ. Say 1,200Wh a day. With losses, that is about 1,400Wh. For one full day you need a station above that, and for two days you need to double it or plan to recharge. Look for capacity that can be expanded and for a rated output well above the fridge's start-up surge. The descriptions mention lifting power and expandable capacity on some larger units.

Example 3: A remote work day

A laptop at 60W for eight hours is 480Wh. Add a monitor at 25W for the same time (200Wh), a router at 12W (about 100Wh) and phone charging (about 30Wh). The total is about 810Wh. With losses, plan on 950Wh or more. That points to a station of around 1,000Wh or larger. If the work cannot be interrupted, the Elite 30 V2 description mentions a 10ms UPS-style switch, though it is a small battery and suits a modem and a laptop rather than a full desk.

How to choose

• Match capacity to your total, with losses added, not to the biggest number on the shelf.
• Check the rated output against your largest load, or the total of what runs together.
• Look at how it recharges: AC, solar, car or generator. The descriptions list which each model supports.
• If you may need more later, look for the expandable models.
• For outage use, check for the pass-through or UPS wording in the description.
• Weight and size matter if you carry it. The Elite 100 V2 description gives 25lbs.

Questions people ask

Is watt hours the same as watts?

No. Watts are how fast a device uses power. Watt hours are how much it uses over time. A 100W device running for two hours uses 200Wh.

Can I use the full capacity?

Plan on less. Conversion losses and a safety margin mean the usable amount is below the label figure. Follow the manual for your model.

Do I need solar?

Not always. For a long trip or a long outage it helps, because it lets you refill the battery. For a single night, a full charge at home may be enough.

What if my total is just above a model's size?

Go up a size, or cut a load. Running a battery near empty every time is a poor plan.