Can You Use Ryobi Batteries On Harbor Freight Tools?

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Like most major hardware brands these days, Ryobi maintains several different battery systems for its various cordless power tools, most prominently the 18V ONE+ framework. However, stocking up on both Ryobi tools and their compatible battery packs can be prohibitively expensive. The batteries alone can easily run for over $100 depending on their specs, and the tools themselves also hover around the same range or higher.

If cash is a concern, you could try Harbor Freight. After all, Harbor Freight's various in-house brands like Bauer and Hercules offer battery-powered tools that generally cost less than Ryobi's, so it'd be a perfect solution. 

Sadly, this solution is a non-starter; due to the particular design choices of Ryobi's batteries, there's no way for them to even be inserted into a Harbor Freight tool, let alone supply power. This limitation could theoretically be overcome through the use of a third-party battery adapter, but doing so would expose your batteries and tools to potential risk.

While every hardware brand that uses rechargeable battery packs with their cordless tools follow the same basic concept, the means by which that power is actually supplied to the tools varies by brand. Most power tool batteries have a panel on top housing power transfer terminals, as well as connecting rails on the sides that allow them to snap securely onto a tool. Ryobi, however, is an outlier in the crowd, as its ONE+ battery packs have a distinct stalk jutting up out of the top.

Let's compare a Ryobi ONE+ 18V 4Ah battery pack to a comparable offering from Harbor Freight, such as a Hercules 20V 4Ah battery. The Hercules battery has a flat panel on top, with several divots housing the power terminals. This battery slides onto a tool via its connecting rails, and the divots line up with the tool's receiver so the terminals can connect. The Ryobi battery, meanwhile, is designed to be inserted directly into a small hole on a Ryobi tool. You can see the terminals on the sides of that jutting stalk, which line up with those in the tool's receiver hole.

Because of this substantial difference in design, there's no way for a Ryobi battery to actually plug into any tool from Harbor Freight. There are no connecting rails to secure the battery to the tool, and the placement of power terminals prevents any power from flowing from the battery to the tool. Naturally, this disconnect goes both ways; you won't be able to plug any of Harbor Freight's batteries into a Ryobi tool either.

There is no native, manufacturer-supported way for a Ryobi battery to plug into a tool from one of Harbor Freight's in-house brands. However, there is a way. Sort of. In the same vein as third-party tools Amazon tools that use Ryobi batteries, third-party brands and individuals make various unofficial adapter accessories that can allow one brand's batteries to plug into another brand's tools. These accessories are typically sold on platforms like Amazon and eBay, as well as dedicated sites like Power Tools Adapters.

While an adapter seems like an ideal fix, though, it comes with two big problems. First, all adapters are strictly one-to-one. That means you can't use one adapter for a Ryobi battery and any tool from Harbor Freight; you'd specifically need a Ryobi-to-Bauer adapter, Ryobi-to-Hercules adapter, and so on.

The second, more pressing problem is safety. Ryobi's batteries are equipped with an internal circuit board that communicates directly with connected Ryobi tools, optimizing the power flow for safe, efficient use. Connecting a Ryobi battery to a Harbor Freight tool via an adapter disables this safety circuitry, forcing energy to flow in an unoptimized state. 

This could result in either low-power performance in the tool, or a dangerous power overload, which could burn out the tool's motor. If either your Ryobi battery or your Harbor Freight tool are damaged while using a third-party accessory like this, that's considered a warranty violation, and neither company will help you.