Compact Vs. Thick Milwaukee M18 Batteries: What's The Difference?

No matter which of the major power tool brands you choose, chances are you're going to end up with battery-powered tools. This technology is prevalent across the tool world at this point, with corded tools mostly a thing of the past. Tool companies have invested heavily in battery tech, increasing their power level, runtime, and heat resistance, among other factors. Milwaukee is one such name, having developed numerous battery types throughout the years to power its ever-expanding catalogue of tools.

Two battery categories present in Milwaukee's 18-volt M18 line — not to be confused with Milwaukee's M12 series — are the compact and thick batteries. Compact batteries, denoted by the CP on the battery, favor portability and a smaller footprint over all else. They are, as their name implies, smaller and more lightweight than other Milwaukee batteries. Meanwhile, thick Milwaukee batteries, specifically its high-demand (HD) and extended-capacity (XC) batteries, are noticeably larger. Naturally, this also means that they're heftier than their CP counterparts, with the HD being bigger and heavier than XC. Moving on from their dimensions, there's more to the differences between compact and thick Milwaukee batteries. There's also the matter of their outputs and ideal use cases.

Milwaukee's compact and thick M18 batteries differ in more areas than just their physical dimensions. Milwaukee's compact batteries have rather low amp hours, ranging from 2Ah to 3Ah, though the latter is considered "high output" and can power more M18 tools than its standard counterpart. Therefore, these batteries overall are best used on tools that don't demand much power and on jobs where they won't be run extensively. If maneuverability is more of a concern than continued use, CP is the way to go.

As for Milwaukee's thick batteries, XC and HD, things look a bit different. Not only is there a much wider selection of XC batteries, but they also come in higher amp hours than CP batteries. They range from 4Ah to 8Ah, and are compatible with over 250 Milwaukee tools. These are considered the most versatile of the M18 batteries out there, finding a middle ground between weight, power, and longevity. The same can't quite be said for HD batteries. They're big and heavy, but they're the most powerful. They come in at 12Ah, offering the most runtime of these M18 battery categories. They're best suited for prolonged use on larger tools where power and runtime are the main priorities.

Milwaukee batteries are known to get expensive, so it's important to know what you're getting before paying up. Fortunately, telling the difference between the brand's M18 compact and thick battery types, CP, XC, and HD, goes a long way in helping determine which is right for you and your needs.