DeWalt 20V MAX XR Cordless Brushless 7 in. Variable Speed Rotary Polisher (Tool Only)

Why this cordless rotary earned a spot in my detailing kit

Cordless polishers are finally mature enough to replace cords in real paint-correction work, and the DCM849B is a good example of why. I’ve been using this 7-inch DeWalt rotary for panel corrections, gelcoat work, and the occasional glass job, and it nails the basics: steady speed control, usable torque at low RPM, and ergonomics that keep you in control for more than a few minutes at a time.

It’s sold as a bare tool, so you’ll need your own 20V MAX battery and charger. A 7-inch backing plate comes in the box; mine arrived with both a side handle and a bail-style handle as well, though availability seems to vary by seller. No case is included.

Build and ergonomics

The housing feels every bit DeWalt—stout without being clunky. The rubber overmold on the gear case isn’t cosmetic; it’s genuinely helpful when you choke up for precise control along edges or on curved panels. The head shape and low-profile nose make it easier to keep pads flat, even with wool.

Weight is often the deciding factor for a rotary, especially when you hang a big battery on the back. On my scale the bare tool landed just over 6 lb; with a 5Ah pack it was about 8 lb. That’s within the normal range for 7-inch rotaries. Balance is surprisingly neutral with 5Ah and 8Ah packs; the tool doesn’t feel wrist-heavy or nose-heavy, and the front grip gives a secure second handhold when you don’t want to use the auxiliary handles.

Fit and finish are tidy. The trigger pull is progressive with a positive detent lock-off. The speed dial has tactile steps and sits where your thumb can find it without contorting your grip. Nothing rattles, nothing buzzes, and the gear mesh remains smooth under load.

Controls and speed management

The rotary’s variable-speed setup is well executed: a dial sets the ceiling, and the trigger modulates within that band. The listed no-load range is roughly 800–2,200 RPM. In practice:

• At the low end, it holds steady around 800 RPM and doesn’t bog easily, even with a damp finishing pad.
• Mid-range (1,200–1,600 RPM) is the sweet spot for correction with foam or wool.
• Top end has enough headroom for gelcoat and glass where you want more bite.

If you’re used to corded rotaries that drop to 400–600 RPM, note that the DeWalt won’t crawl quite that slow. You can feather the trigger to momentarily dip below the dial setting when placing the pad, but sustained “super-low” jeweling is limited by the 800 RPM floor. That said, pad control is stable at the bottom of its range, and I had no problem finishing on medium-hard clear with a soft foam and a fine polish.

Power and cut

This brushless motor is more about consistency than brute force, and that’s the right choice. It doesn’t surge when you bump the trigger, and it resists stalling when you lean into curved panels or tilt slightly to ride an edge. The torque delivery feels linear, which makes it easier to maintain pad flatness and pressure.

Correction performance was predictably pad- and product-dependent. Some real-world notes:

• With a 7-inch wool cutting pad and a diminishing-abrasive compound at ~1,400 RPM, I removed moderate defects on hard German clear in two passes, then followed with a foam finishing pad at 1,000–1,200 RPM to clean up.
• On oxidized gelcoat, a twisted wool pad and a heavy compound at 1,800–2,000 RPM gave fast results without the motor hunting for speed.
• For glass water spots, a rayon pad and cerium delivered controlled cut at 1,600–1,800 RPM, with the tool staying planted and predictable.

Vibration is low for a rotary this size, assuming your pad is centered. The rubberized head keeps your lead hand insulated when the gear case warms up during longer sessions.

Runtime and batteries

Runtime always depends on how hard you lean on a rotary. My averages:

• 5Ah battery: roughly 18–25 minutes of continuous polishing at moderate pressure and ~1,300 RPM, more if you’re doing light finishing.
• 8Ah battery: around 30–40 minutes under similar conditions.
• FlexVolt 6Ah pack: similar to an 8Ah 20V MAX in feel and duration, with a bit less voltage sag on heavy cut.

The takeaway: one 5Ah pack will get you through a panel or two; two packs in rotation make full-vehicle work practical. If you’re moving from corded, plan your workflow—swap batteries during wipe-downs or pad changes to avoid waiting on a charger. The brushless drive is efficient, and the tool doesn’t roast packs; they come off warm, not hot.

Noise sits in the typical rotary band—gear whine plus pad-on-panel—you’ll still want hearing protection in enclosed spaces.

Pad and plate compatibility

The spindle is the standard 5/8"-11, so any mainstream 7-inch plate drops on. The included 7-inch hook-and-loop plate is flat and true. For tighter spots, a 5-inch plate works fine and reduces tool mass in the nose, but keep in mind you’re still wielding a full-size rotary—there are limits to how “small” it can feel.

I had good results with:

• 7-inch wool (fast correction, watch your edge angles)
• 6–7-inch foam cutting and finishing pads (balanced, easier to finish on)
• Rayon/glass pads for mineral deposit removal

As always, use fresh pads; imbalance is what makes rotaries feel harsh.

Practical use cases

• Paint correction on medium-to-hard clear coats where rotary speed and bite save time.
• Oxidation removal on gelcoat and fiberglass, where cordless convenience around a boat or RV is worth its weight.
• Headlight restoration and glass polishing, especially when an extension cord is impractical.

If you’re new to rotaries, practice on a test panel. This is a direct-drive tool; it cuts fast but can also haze or hologram if you’re sloppy with pad angle and pressure. I often finish with a dual-action polisher after heavy rotary correction on softer paints.

What I like

• Cordless freedom without sacrificing usable torque at low RPM.
• Thoughtful controls: a true speed cap on the dial and a progressive trigger.
• Stable pad control; low vibration and good balance with common battery sizes.
• Brushless efficiency; batteries don’t cook, and the motor doesn’t hunt under load.
• Standard 5/8-11 spindle and an included 7-inch plate make setup simple.

Where it could be better

• No case in a tool-only kit; storage and transport are on you.
• The 800 RPM floor is fine for most work but not for ultra-slow jeweling fanatics.
• As a full-size 7-inch rotary, it’s not the best choice for tight contours or body lines—consider a smaller plate or a compact machine for those.
• Price plus the need for at least two batteries can add up if you’re starting from scratch.

Who it’s for

• Detailers and DIYers who already own 20V MAX packs and want a serious rotary without the cord.
• Marine and RV users who value mobility and quick correction on large surfaces.
• Experienced polishers who understand rotary technique and want predictable, steady speed with minimal fuss.

If you’re new to paint correction or you primarily finish on very soft paints, a dual-action polisher may be a safer starting point. This DeWalt plays nicely alongside a DA: use the rotary for rapid cut, then refine with the DA.

Recommendation

I recommend the DCM849B for anyone who wants a well-mannered, full-size cordless rotary that behaves like a good corded machine but without the tether. It delivers consistent low- to mid-range speed, solid torque, and confidence-inspiring ergonomics. Plan on at least two batteries for continuous work and accept the 800 RPM minimum as part of the package. If you can live with those constraints—and especially if you’re already on DeWalt’s 20V platform—this polisher is a practical, reliable addition to a professional or serious enthusiast kit.