Are Harbor Freight Batteries Compatible With DeWalt's Tools? Here's What We Found

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It's the moment of hope that makes the disappointment all the more harsh. You look at the two things side by side, and they seem to be physically identical: a $110 DeWalt 20V Max 5Ah battery pack and a Harbor Freight (HF) Hercules battery with the same specs, but for $50. Wouldn't it be quite a coup if the HF battery worked on the DeWalt tool?

But they won't work together, and it might not be a great idea even if they did. This is because the HF Hercules batteries, which the company itself compares to DeWalt tools, don't really stack up well to DeWalt's batteries in some important ways. While the construction of the Hercules batteries is actually quite good, the cells themselves seem to fall short of their own advertised capabilities. For example, tool and battery teardowns have shown that a 2.5Ah Hercules battery only delivers around 1.69Ah.

There are ways to get cheaper batteries into your DeWalt tools, but they all have drawbacks — sometimes, safety drawbacks. Toolmaker Mellif claims some compatibility with DeWalt batteries and plans for charger compatibility. You can also buy cheap knockoff batteries that appear to be fully compatible with DeWalt tools, and even counterfeit DeWalt tools and batteries on Amazon and elsewhere, and while some have reasonably good performance in terms of power delivery, they can be missing key features like overcurrent protection to protect against thermal runaway (the dangerous process that can cause lithium-ion batteries to catch fire). They can also lack mechanical protection and have subpar battery and tool protection.

Out of the box, Harbor Freight batteries (including Harbor Freight's popular vaguely comparable Hercules power tool line) simply will not fit into DeWalt tools, and vice versa. They are designed this way intentionally, probably for both safety and profit-protection reasons. Although they are visually very similar, a close comparison reveals that the sliding rails and contact configurations of the batteries are different enough to render them incompatible.

But even if you bypass the physical mechanisms that prevent HF batteries and DeWalt tools from working together, they still won't functionally work. Wiring a Hercules battery directly to the matching contacts on a DeWalt tool yields, well, nothing at all. Some have claimed that there are smart electronics that communicate directly between manufacturers' batteries and tools, so that mismatched components are prevented from working together. 

But the real mechanism turns out to be much simpler than that, as we explain below. However, any protective circuitry on the tool side might be missing on a mismatched tool, and create quite a hazard. In older Hercules batteries, at least, there's simply a different configuration for a safety mechanism that keeps them from being electronically compatible.

There are two ways to make Harbor Freight batteries work with DeWalt 20-volt tools. YouTuber jimbob (@mosesdog2) figured out why the batteries weren't interchangeable: The mechanism by which the batteries report their temperatures to the tools uses different terminal pins and different scales. To get around this, you first need to use a tool like a Dremel to modify the Hercules battery so it mostly fits the tool. Then you'd disassemble the Hercules battery and solder a particular resistor between two of its contacts — a delicate operation, given that you're heating a nickel strip attached to a battery technology prone to thermal runaway and catching fire when mishandled. Assuming the hack works for you, you'll gain an ill-fitting battery that powers your tool, but which also circumvents the thermal protection that makes lithium-ion batteries safe enough to use.

There's one more avenue available to you to make Harbor Freight batteries work with DeWalt tools. Adapters for Harbor Freight's Bauer and Hercules batteries are available, like the TPDL Adapter for Bauer 20V Li-ion (which you can also find on eBay). But, since HF and DeWalt batteries' mechanisms are different, it's very unlikely that either adapter offers thermal protection. The Hercules adapter is described as having a multilevel protection function, with no specifics provided, but its product description does warn against using it in a high-temperature environment. This could be because the 3D-printed adapter is made of PLA or another temperature-sensitive material, or because it lacks built-in protection. The Bauer adapter doesn't mention any protections at all. On the whole, you might want to wait for a sale and just buy new DeWalt batteries.