Which lasts longer per charge?

The 4.0Ah BL1840B. It has twice the capacity of the 2.0Ah, so expect roughly double the runtime in the same tool.

Is the 4.0Ah worth the extra $29?

Yes if you use saws, grinders or other high-draw tools, or work far from a charger. For light drilling and driving, the 2.0Ah is enough and saves money.

Which is better for overhead work?

The 2.0Ah. At about 380 g it is roughly 260 g lighter, which matters when you hold a drill above your head.

Do both fit the same tools and chargers?

Yes. Both are 18V LXT packs and work with Star Protection tools and Makita LXT chargers. The 4.0Ah charges in 40 minutes or less on the Rapid Optimum Charger.

Which handles cold weather better?

The 4.0Ah. Makita rates it for use down to -4°F/-20°C; the 2.0Ah has no published cold-weather rating.

Can I use the 2.0Ah as a spare for the 4.0Ah?

Yes. They are interchangeable, so a 2.0Ah makes a light backup while the 4.0Ah recharges.

Makita 18V LXT 4.0Ah Battery BL1840B vs Makita 18V LXT 2.0Ah Battery

Buy the 4.0Ah BL1840B if you run high-draw tools like circular saws, grinders or recip saws, or work long shifts away from a charger. Buy the 2.0Ah BL1820B if you want a light pack for drilling, driving and overhead work, or a cheap spare. As of November 7, 2026, the 4.0Ah is $76.97 at eBay and the 2.0Ah is $47.95 at Amazon, so the bigger pack costs about $29 more for roughly double the capacity.

Today the Makita 18V LXT 2.0Ah Battery costs $29.02 less at its best price.

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