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Home ยป Power Tool Batteries: What are Amp-hours (Ah)?

Power Tool Batteries: What are Amp-hours (Ah)?

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DeWalt Battery

So you’re shopping for cordless power tools and you see a bunch of different combo kits/batteries with different Ah ratings. What does it all mean?

Basically, amp-hours indicate the capacity of the battery in terms of how long it will last on one charge.

More technically, amp-hours are a measurement of electric current (amps) multiplied by time, equal to the amount of amps that flow in one hour. There are many articles around that go into too much detail, so I’m going to keep this simple.

How many Ah do I need for my cordless power tools?

There is no simple way to determine this — it would be easy if every tool drew 1 amp, for instance, but different tools/brands draw different amounts of power. Here is what we know for sure:

  • Larger power tools that do more work will draw more current, i.e. a belt sander will draw more current than a drill
  • Since larger power tools draw more current, you’ll run out of battery capacity quicker with these tools
  • Since you’ll run out of battery capacity quicker with this tools, it makes sense to use larger batteries for larger power tools

Based on this information, it makes sense that you should get larger-capacity batteries for tools that have larger power needs. I recommend that you have at least 2 batteries on hand so that you can use one while the other is charging.

I have 3 cordless tools: a drill, orbital sander, and jigsaw. I don’t use these tools for prolonged amounts of time (except maybe the sander), so I have been able to get by with two 2Ah batteries. If one gets close to the end of its charge, I just swap it with the fully charged one. I also like having a smaller-sized, lighter-weight battery with these tools — for me it would be inconvenient to have huge clunky batteries on these tools. With these tools, I would not recommend a battery under 2Ah.

For larger tools, like a circular saw, belt sander, or a reciprocating saw, I’d go with at least 5Ah to ensure you can complete your project with one battery, and the second as a backup in case you need more runtime.

I hope this helps to simplify the complex world of batteries!

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