Battery amp hours can really affect how much power your power tool can deliver
In our Craftsman vs. Ryobi hammer drill comparison, some people pointed out that we used different batteries: 2.0Ah for the Craftsman and 4.0Ah for the Ryobi. Since most people buy these tools as a kit, we tested kit batteries. However, most tool enthusiasts know that battery amp hours affect power. But how much?
First, to those who commented, thank you for the maturity you have shown in the tone of your comments. How refreshing that we, as fellow human beings, can be treated like this!
To resolve this apparent controversy, we used Makita 18V LXT 2.0Ah and 5.0Ah batteries. We wanted to see how much of a power difference the larger 5Ah pack made. We chose a Makita XPH07 drill to help us with our testing.
Voltage vs. Amp Hours 101
Both 18V and 20V Max batteries use 5 cells per bank to achieve 18 nominal voltage. Each cell contributes 3.6 volts (4.0 volts max), and connecting them in series brings the total voltage to 18 volts (5 x 3.6).
The Makita 2.0Ah battery uses only one row of 5 cells. The 5.0Ah battery pack uses two rows of battery cells connected in parallel. This keeps the voltage at 18, but doubles the amp hours to 5.0.
But there is more to the story.
You see, the amp-hours of a 5.0Ah battery pack are actually more than double that of a 2.0Ah pack. That's because they use different cells. They are both 18650 size but have different energy densities. So, in addition to having double the number of cells, the 5.0Ah battery also has a higher energy density .
Generally speaking, higher amp hours means longer run time, and higher voltage means more power.
Read more about the relationship between voltage and amp-hours.
Makita 18V LXT 2.0Ah vs 5.0Ah Battery Comparison
- Model: BL1820B
- Lithium-ion battery: 5
- Weight: 0.8 lbs
- Charging time: 25 minutes
- Model: BL1850B
- Li-ion battery: 10
- Weight: 1.4 lbs
- Charging time: 45 minutes
High Speed Test: 1 Inch High Speed Auger Bit
We like to use stacked OSB subfloors as our test material because of its consistency. Drilling through 5 layers isn't exactly a real world application, but it can solve problems caused by knots or other inconsistencies in the wood. We started drilling with a 1" Bosch Daredevil high speed auger bit to test the effect of battery amp hours on power.
With those super smooth bits, the 5.0Ah battery has a slight edge, 4.33 seconds to 4.48 seconds.
5.0Ah power boost: Drilling speed increased by 3.35%
High Speed Test: 1" Spade Bit
We stuck with the same material while switching to 1" Bosch Daredevil Spade Bits for the next test. These don't drill as smoothly, and they require a bit more power than auger bits. Still, we can drill at high speeds with ease.
The small gap between the two batteries we saw in the first test widened with the spade bit, from 3.59 seconds to 4.00 seconds.
5.0Ah power boost: Drilling speed increased by 10.25%
Low Speed Test: 1 1/2" Self Feed Drill
We also switched to a pair of untreated 2 x 4s for our material when we got into low speed testing. We started with a 1 1/2" Milwaukee Switchblade self-feeding bit.
As the power demands of new drills continue to increase, the gap between the two batteries' drilling speeds continues to widen. The 5.0Ah battery takes 10.28 seconds, while the 2.0Ah battery pack takes 12.08 seconds.
5.0Ah power boost: Drilling speed increased by 14.90%
Low Speed Test: 2 9/16" self-feeding drill
The last test we did was with a 2 9/16" Switchblade and required more power from the drill. Here again, the 5.0Ah battery demonstrated its ability to deliver more power to get the job done, taking 11.26 seconds compared to 14.60 seconds for the 2.0Ah.
5.0Ah power boost: Drilling speed increased by 25.88%
Battery amp hours affect power, but why?
Theoretically, if both battery packs are supplying 18 volts, it won't affect power, just run time. A closer look at package design can provide some insight. Power is measured in watts, which you can calculate by multiplying volts and amperes.
The drill actually requires 18V from both batteries, so it stays the same. Where the battery count comes into play is in amps (current). Let's say the Makita XFD07 needs 360 watts of power to drill the next hole. At 18V, each cell needs to deliver 20 amps to do this (18V x 20A = 360W).
Each cell in the series has to supply the full current as it doesn't add up across the series connections. The 5 cells in the 2.0Ah battery pack need to supply 20 amps each. In a 5Ah battery, there are two sets of cells, and the parallel connection between them does add the current. Therefore, each group only requires 10 amps from each of its cells.
With 10 cells, it's much easier to run each cell at half strength to maintain power levels. The tougher the task, the harder it will be for a 5-cell battery to maintain the same power level as a 10-cell battery.
The situation is similar when you test the runtime. In theory, a 4.0Ah battery should run twice as long as a 2.0Ah battery. However, you actually get much more than that. We've found that amp-hours affect run time to a large degree.
the bottom line
Now that we know how much battery amp hours affect power, the application side is pretty straightforward. In lighter tasks, there isn't much advantage to a bigger battery, so save some weight and opt for a smaller battery pack. The difference is huge when you get into medium and heavy duty applications, where higher capacity batteries are the sweet spot.