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
Milwaukee 3/4″ spade bits
Milwaukee 2404 M12 Fuel Hammer Drill
Milwaukee M12 2.0Ah and 4.0Ah battery
Milwaukee M12 Charger
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.
Procedure: How We Test to See How Amp-Hours Affect Battery Runtime
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
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.
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!
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
