October 23, 2021

Professional Tool Reviews for Pros

How Amp-Hours Affect Battery Runtime

Do You Get Twice the Runtime From Twice the Amp Hours?

The 5th-grade science fair came around for our school and finding a project to use power tools sounded much more exciting than anything else. It’s a good thing my Dad is the Managing Editor of Pro Tool Reviews. I decided to tackle the question, “how amp-hours affect battery runtime?”. Another way to say it is do you get twice the runtime from twice the amp hours?”

It boils down to this: a 4.0 Ah battery has exactly twice as many watt-hours as a 2.0 Ah battery. So in theory, the 4.0 Ah battery will do exactly twice as much work. But is that really the case?

Not only is it a question I wanted to know the answer to, but it’s also one that Pro Tool Reviews hasn’t written an article for. Well, the science fair is over, so now I get to write an article to share what I discovered.

Materials Needed to Test How Amp-Hours Affect Battery Runtime

2 x 6 pressure treated pine

how amp-hours affect battery runtime

Milwaukee 3/4″ spade bits

how amp-hours affect battery runtime

Milwaukee 2404 M12 Fuel Hammer Drill

Milwaukee M12 2.0Ah and 4.0Ah battery

Do You Get Twice the Runtime From Twice the Amp Hours?

Milwaukee M12 Charger

how amp-hours affect battery runtime

Ryobi One+ 18V Hybrid Fan

Variables that Affect Tool Battery Runtime

Constant Variables

  • 4 x 6 PT
  • 3/4″ Spade Bits
  • Milwaukee M12 Fuel Hammer Drill
  • Milwaukee M12 Charger

Independent Variables

  • Milwaukee M12 2.0 Ah Battery
  • Milwaukee M12 4.0 Ah Battery

While the 4 x 6 PT goes into my constant variable list, it’s not actually as constant as I would like it to be. All lumber has slight variances in density throughout it. There are also knots, but we can see those easily and will work around them.

how amp-hours affect battery runtime

Procedure: How We Test to See How Amp-Hours Affect Battery Runtime

Do You Get Twice the Runtime From Twice the Amp Hours?

Scientifically speaking, writing a procedure on how amp-hours affect battery runtime is pretty detailed. But that makes for boring reading, so it looks a little different than my project board does.

The idea is to drill 10 holes into the PT using a 3/4″ Milwaukee spade bit, switch batteries, then drill ten holes with the other. You keep swapping batteries to make sure that they don’t get too hot. If they do, the drill’s electronics will shut the whole thing down and make you think the battery is dead even if it isn’t.

Be sure to avoid drilling in any knots.

Once the first battery dies, you drill 10 holes with the remaining battery, take it out, and set it in front of a fan for 1 minute to let it cool. Keep going until the second battery is dead.

While you can get some impressions from one test, it’s not enough to satisfy a science fair project. When the batteries are both dead, charge them back up and start over until you’ve done the experiment 5 times. You might want to grab a sandwich or go to the park for a bit while the batteries charge. They can take more than an hour and it’s kind of boring to sit and wait on it.

A multi-port fast charger like Milwaukee’s M18/M12 charger helps.

And of course, be sure to write down your results!

Hypothesis: Does Doubling the Amp-Hours Double Battery Runtime?

The 4.0 Ah battery will do more than twice the amount of work as the 2.0 Ah battery because the smaller battery will have to work harder to do the same job.

Results: Here’s What Happened

how amp-hours affect runtime

Test 1

  • 2.0 Ah holes: 55
  • 4.0 Ah holes: 121

55 x 2 = 110

The 4.0 Ah battery did 11 more holes than twice the 2.0 Ah battery

Test 2

  • 2.0 Ah holes: 59
  • 4.0 Ah holes: 116

59 x 2 = 118

The 4.0 Ah battery did 2 fewer holes than twice the 2.0 Ah battery

Test 3

  • 2.0 Ah holes: 50
  • 4.0 Ah holes: 111

50 x 2 = 100

The 4.0 Ah battery did 11 more holes than twice the 2.0 Ah battery

Test 4

  • 2.0 Ah holes: 48
  • 4.0 Ah holes: 99

48 x 2 = 96

The 4.0 Ah battery did 3 more holes than twice the 2.0 Ah battery

Test 5

  • 2.0 Ah holes: 45
  • 4.0 Ah holes: 97

45 x 2 = 90

The 4.0 Ah battery did 7 more holes than twice the 2.0 Ah battery

Conclusion: Do You Get Twice the Runtime from Twice the Amp Hours?

On average, the 4.0 Ah battery does more than twice the work of a 2.0 Ah battery. We did have one test where it did less, though. This supports my hypothesis.

Do You Get Twice the Runtime From Twice the Amp Hours?

Editor’s (AKA Dad’s) Notes

Taking the results of all 5 tests together, the 2.0 Ah battery bored 257 holes. The 4.0 Ah battery bored 544 holes. If the 4.0 Ah battery only did twice the work, it should have drilled a total of 514 holes. As it stands, it does 5.5% more work than the amp hours/watt hours suggest on paper.

There’s a reason for this. A 12V, 2.0 Ah battery operates on 3 lithium-ion cells. The 4.0 Ah battery has 6. However, they’re both producing 12 volts, meaning each member the 6-cell system only needs to deliver half the current (amps) that each member of the 3-cell team does. Since each cell doesn’t have to work as hard, it’s able to work more than twice as long.

The same goes for any voltage battery where you have multiple amp hour options. We expect the runtime to do more than match the increase in amp hours in the same applications. You’ll also notice similar changes as you move from 18650 cells to 20700 or 21700 cells. The bigger cells work more efficiently on an individual cell level, so they give you more work than you expect on paper.

5th Grade Science Fair Results

For my efforts, I won 2nd place in our school Science Fair!

Amp-hours vs Battery Runtime Shoutout

Thank you to Milwaukee Tool for providing the 2504-22 M12 Fuel Hammer Drill Kit, batteries, and spade bits. Not only is it a great tool to use, but the fact that it comes in a Milwaukee PackOut box is really cool!

Do You Get Twice the Runtime From Twice the Amp Hours?

Milwaukee M12 Fuel Hammer Drill Kit Features

  • Milwaukee Powerstate brushless motor
  • M12 RedLithium battery technology
  • RedLink Plus electronic communication
  •  18-Position clutch
  •  Hammering action delivers up to 25,500 IPM in high speed and up to 6750 IPM in low speed
  •  Compatible with all Milwaukee M12 lithium-ion batteries (2.0 Ah battery included in kit)
  •  LED light illuminates workspace
  •  PACKOUT compact organizer

Milwaukee M12 Fuel Hammer Drill Specifications

  • Model: Milwaukee 2504-22
  • Power Source: Milwaukee M12 battery
  • Voltage: 12V
  • Max Torque: 350 in-lbs
  • No Load Speed: 0 – 450/0 – 1700 RPM
  • Impact Rate: 0 – 6750/0 – 25,500 BPM
  • Warranty: 5 years
  • Price: $179

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Thank you for this write-up! Good info, and well written!


I mean, it’s not even a review…


I think the most impressive result is that a common 3/4″ Milwaukee spade bit was able to drill so many holes in pressure treated pine without dulling. The salts used to make the pine board rot resistant (copper quats) often contribute to rapid erosion of the ferrous metals used in those heat treated spade bits. So switching back and forth between the battery packs also helped to randomize the effects of the spade bit dulling and requiring more power to complete each hole. Good job on getting your kid to drill so many holes to make the results statistically valid.


Great job! This phenomenon is definitely a little known, little understood fact. The cells in the test batteries, likely Samsung INR 18650 20Rs, achieve 1.9 amp hours at 10A draw, 1.85 at 20A and 1.55 at 30A. So clearly, when you double the cells to half the load, you get more actual capacity. Note they don’t actually get 2.0 amp hours, because that is measured at only a 2A draw.

Mike Zee
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