If you look up the name of your drill in any shop, you will find forty listings, half of which are labelled 'universal' and none of which are convincing. The incorrect method is to start by looking at the tool; the correct one is to begin with the battery lying on your bench.
In short, you should purchase the battery using the model number specified by the battery itself, and then check four things in turn—voltage, platform, connector, and capacity—before evaluating the seller. It involves five steps and takes approximately ten minutes, guaranteeing that you'll always receive the same result.
The following is a step-by-step guide on how to select a replacement battery for your power tool. You'll find out where the model number is located, which features you need to match and which ones you can choose freely, and how to interpret a battery listing so that you never have to order the wrong battery twice. If you prefer just the brief version of all this, then our electric tool battery guide contains the short form.
Step 1: Find the battery's model number
The battery has its own identity and is not the same as the name of your drill. A kit number refers to the kit, including both the tool and the batteries it contains, while the battery itself has a separate number which is printed on its label.
Where to look, in order of likelihood:
- The bottom of the pack. Most common by far.
- The side specification label.
- The top surface, near the slide rails or the release latch.
What to copy when you find it:
- Model No. or Part No. / P/N, every character, hyphens and suffixes included. A trailing letter usually marks a generation, so a number that ends in B is not the same battery as the number without it.
- Not the voltage and Ah by themselves. 18V and 5.0Ah are specs that thousands of batteries share. They help, but they don't identify yours.
Take a photograph rather than making notes; people always send us pictures of the way in which they are drilling, and it is the picture of the battery label that has the answer.
Real numbers appear as for example DCB546 or 499948-03, depending on the manufacturer, and that string is the one you type or send when you're shopping. By the way, you only need one model number. If a listing says that it will fit a dozen different part numbers, it's effectively claiming to be a dozen different batteries at the same time, and that's your first red flag before you've spent a single cent.
Step 2: Match the voltage and the platform
Voltage is non-negotiable. An 18V tool takes an 18V class pack, and that's the end of the discussion.
The label confusion gets its own sentence, because it trips up more buyers than anything else. DeWalt's official pages state that 20V MAX is a 20-volt peak measurement of the same 18-volt nominal pack, so when you shop, treat 18V and 20V MAX as one class, not two.
Then there's the platform trap, and it catches people who did the voltage right. Same brand is not enough. Same platform is what matters:
| The trap | What actually happens |
|---|---|
| Milwaukee M18 vs M12 | Two separate systems. An M12 pack does not fit an M18 tool. |
| Ryobi ONE+ 18V vs 40V | Separate connectors, separate tools. They do not mix. |
| DeWalt 18V stem vs 20V MAX slide | The old stem packs and the new slide packs are different systems. |
The Power Tool Institute explains why the walls exist: each brand's packs carry proprietary control circuitry that only talks to its own tools and chargers. So verify the platform name on the listing, not just the brand name.
Step 3: Match the connector
Now look at the physical shape. Slide packs ride on rails. Older post packs plug in on a stem. They don't swap, and a pack that looks right in a photo but sits loose or won't click is the wrong connector no matter what the listing says.
Check the slot geometry and the locking mechanism when you compare listings, and check the photo against your own pack from the same angle. The full anatomy of tool battery connectors, including why cross-brand adapters are a gamble, lives in our power tool battery compatibility guide.
Step 4: Pick the capacity band
Capacity is the one thing you're allowed to choose. Voltage and connector get matched. Amp-hours get selected, and the selection is about how you work.
| Your work | Band | Why |
|---|---|---|
| Weekend screws, shelves, light fixes | 1.5 to 2.5Ah | Light, cheap, and a full charge covers a lot of small jobs |
| Renovation, trimmers, half-day projects | 3.0 to 4.0Ah | The middle ground. Long enough for real work, light enough to hold overhead |
| Saws, blowers, all-day use | 5.0Ah and up | Maximum run time, with the extra weight and cost that come with it |
The honest middle-ground opinion: for most home users, the 3.0 to 4.0Ah band is the buy. A 6.0Ah pack is a better battery on paper, but if your Saturday projects run two hours, that pack spends most of its life at half charge waiting for next weekend, and you carried the weight for nothing.
If you want the numbers behind what Ah actually means, we have a plain-English explainer on what amp hours mean.
Step 5: Screen the seller
This is where the money either stays in your pocket or walks. Run this checklist on any listing before you order:
- More than one model number. A real pack is one battery, not a wall of part numbers.
- "Compatible with" three or four brands. Same reason. No honest seller claims one pack fits everything.
- Capacity that doesn't fit the case. An 8.0Ah claim in a slim 2.0Ah-sized case is fiction. You can't hide cells.
- Photos of the box, not the battery. If they won't show the pack itself, there's a reason.
- A price that's half of everyone else's. The Power Tool Institute's rule covers this one: if it sounds too good to be true, it probably is.
- No warranty mentioned anywhere. A seller with nothing to promise is promising nothing.
Half the emails we answer start with a photo of a listing that passed five of six checks, and the one it failed is always the price. It's never the model number. People are careful about the number and optimistic about the price.
On the warranty, ask three questions before you buy: how long is it, what does it cover, and who handles the return. If the listing can't answer those three questions now, imagine asking them after the sale.
Then send the seller these five lines and see how fast a real person answers:
- The model number from your old pack, the whole string.
- The voltage and the Ah.
- A photo of the connector, from the top and from the side.
- The tool it powers, with that tool's model number.
- Where you're shipping it.
If factory versus compatible is the decision you're actually stuck on, our OEM vs aftermarket power tool batteries comparison has the trade-offs laid out. When you're ready, you can browse replacement batteries by brand across the twelve platforms we stock.
Common questions about choosing a replacement battery
How do I know what replacement battery my drill needs?
Find the model number on the old battery itself, usually on the bottom or a side label, and match that. The drill's name is a starting point, not the answer, because one tool line can span several battery platforms.
Are all 18V batteries interchangeable?
No. Voltage is only the first requirement. The connector and the brand's platform also have to match, and each brand walls its platforms off from the others.
Can you replace the battery in a cordless drill?
Yes. Drill batteries are packs that slide or plug out, and replacements are sold for every major platform. The work is in picking the right one, not in the swap itself.
Do off-brand replacement batteries work?
Good ones do, on the platforms they're actually built for, and the screening rules above separate them from the bad ones: one model number, believable capacity, real photos, a stated warranty. For light home use they're a legitimate money saver, and for daily professional use, a factory pack's tested-as-a-system assurance is worth the premium.
How much does a replacement battery cost?
Factory packs cost the most, and the price climbs with capacity. Compatible replacements run well below factory prices, and the 3.0 to 4.0Ah band is where most home users land. Prices move, so compare listings against each other rather than against a number from memory.
To get the right replacement battery you only have to write down one figure and not alter any of the others. First find the model number, then match the voltage and the platform, make sure the connector is the same, choose a capacity range, and then check the seller. Ten minutes spent doing it in this way is better than spending forty minutes looking through listings making guesses, and in the worst case scenario you'll have paid a bit more for capacity than you actually needed.
References & Sources
- Power Tool Institute battery safety and counterfeit battery guides (Power Tool Institute, the power tool industry's safety association)
- DeWalt official site (the 20V MAX nominal voltage footnote on DeWalt product pages)
- Black & Decker service parts (battery part number reference used in the examples above)
Need a replacement?
If you've got the model number, browse replacement batteries by brand. For twelve different tool platforms we offer compatible sets so that you never have to worry about the parts matching, and if you have any questions you can direct them to a real person via our contact page.