What an Inverter Does in a Battery System

The inverter makes a battery's stored power usable. A battery holds one kind of electricity, while your lamps, fridge and phone chargers expect another. The inverter bridges the two. Simple.

The one job it's named for

A power inverter is an electronic device that "changes direct current (DC) to alternating current (AC)"¹. Batteries hold DC, where the current flows in one steady direction². Household outlets deliver AC. So without an inverter, the battery can't run an ordinary appliance.

If you've heard of a rectifier, it's the reverse. Inverters do "the opposite of rectifiers", which turn AC into DC¹. A battery system often needs both jobs, one on the way in and one on the way out. Which parts do which varies by product, so the manual's block diagram is worth a look.

The next page, DC and AC Power, explains why the two kinds differ.

What else it may do

In a household solar setup, the inverter does more than convert. The U.S. Department of Energy says it can also "monitor the system and provide a portal for communication with computer networks"³.

Not every inverter does everything. A small unit inside a portable power station may only convert. A larger home battery inverter may also talk to your solar panels or to the grid, which is a different job entirely and one the spec sheet should spell out. Read it before you assume.

What it outputs

The inverter makes AC at a set frequency. That frequency is usually the same as the standard power line frequency where it's meant to be used¹. A unit built for one region may not suit another, which is why the label matters.

It also makes a certain waveform, meaning the shape of the AC. Some inverters make a smooth curve, others a stepped one. See pure and modified sine wave for the difference.

Questions worth asking before you buy

Think of the inverter as a limit on what you can run. The battery says how long power lasts. The inverter says how much you can run at once, and those are two different numbers that are easy to mix up when you're comparing products side by side.

• What's the continuous output rating, and is it in watts or VA? The difference is covered under watts and VA.
• Is the output pure sine wave or something else?
• What voltage and frequency does it produce, and do they match your appliances?
• Does it only convert, or does it also charge from solar or the grid?
• Is it built into the battery, or a separate box?

If a product is permanently wired into a home, that's licensed electrician work. Don't attempt it yourself, and follow the maker's manual for your own model.

Read each answer from the maker's manual or spec sheet, not from a shop listing. A manual is a source you can check. A sales page is written to sell.