Which one should I buy first?

Buy the impact driver first if you are assembling, framing with screws or doing trim. Buy the saw first if you are breaking down lumber and sheet goods. Most buyers eventually want both because they share the same 20V MAX batteries.

Can I use the same battery on both?

Yes. Both run on DeWalt 20V MAX lithium-ion packs. The driver kit ships with a 5.0Ah battery and charger; the saw ships bare, so that battery can power it once you own it.

Is the saw worth it at $99 if I need batteries?

Only if you already own 20V MAX packs. Add a battery and charger and the real cost climbs well past the $99.00 Amazon price as of November 4, 2026. The driver kit at $136.99 at eBay as of November 4, 2026 includes both.

Which is better for overhead work?

The impact driver. It is compact and light enough to run one-handed, while the saw weighs 8.4 lb and is awkward above shoulder height.

Does the driver have enough power for lag screws?

Yes. At 1,825 in-lbs it drives large-diameter screws and lag bolts that lighter 18V drivers stall on. Use the lower speed settings for smaller fasteners to avoid stripping.

How deep can the saw cut?

2-1/8 in. at 90 degrees and 1-5/8 in. at 45 degrees. That covers 2x material at both angles with the included 6-1/2 in. carbide blade.

DeWalt 20V MAX XR Brushless 1/4 in. Impact Driver Kit (DCF845P1) vs DeWalt 20V MAX Circular Saw dcs391b

These are different tools, not substitutes. Buy the DCF845P1 impact driver if you need to drive screws and lag bolts; buy the DCS391B circular saw if you need to cut lumber. The driver kit is $136.99 at eBay as of November 4, 2026, and includes a 5.0Ah battery and charger. The saw is $99.00 at Amazon as of November 4, 2026, and is tool only, so add a battery and charger if you don't own 20V MAX packs.

Today the DeWalt 20V MAX Circular Saw dcs391b costs $37.99 less at its best price.

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