You have a tool that appears to be the right one and a set that it ought to fit into, yet it doesn't. The shapes are almost identical and the voltage is the same, but still nothing fits together. There's an explanation for this, and it's not because of poor manufacturing; it's the other way around.
Battery compatibility with power tools depends on two types of locks. The first is physical and involves the fact that slide packs and post packs cannot be used together. The second is electronic in that each brand's battery only communicates with its own tools. Batteries can be used interchangeably within a single brand and a single platform, but not when it comes to different brands, and adapters do not provide a safe solution to this problem.
The guide is written in simple English and looks at the two types of connector, the chip which locks each battery pack to its own brand, the rules that apply within each brand's system, the actual cost that adapters impose, and provides a 30-second check when considering any battery pack. Information on voltage and amp-hours can be found in our electric tool battery guide.
The two shapes: slide and post
The two fundamental shapes in the cordless world are as follows.
Slide packs are supported by two parallel rails and secure themselves with a latch. Almost all modern 18V or 20V battery platforms make use of them. The older design, known as the post pack, is plugged into a plastic stem which projects from the battery, the contacts being located either in the stem or on pads surrounding it.
The difference between brands lies in the shape of the rails, the number of notches, and the design of the latch. Two packs may appear exactly the same in a photograph and yet still not be interchangeable because the distance between the rails differs by a few millimeters.
Ten times out of eleven people send us photos showing two packs side by side and asking why they can't be interchanged, and in those cases the answer is already in the photo since the shapes are cousins rather than twins.
Same shape, still no fit: the chip inside
The part that is out of sight doesn't work even if the plastic fits.
All brands incorporate their own control circuitry into the pack, and the tool and the charger continuously communicate with that circuitry, keeping an eye on the voltage, the current, and the temperature. The Power Tool Institute makes it clear that each manufacturer's circuitry is proprietary and that batteries will not be used across different brands unless the tool maker allows it.
The most common trap is that it makes no difference if a company is owned by another. DeWalt and Black+Decker are under the same parent company, yet their battery systems cannot be used together. The platform of one brand doesn't even work with that of the same brand, which is the reason that a brand can offer both an 18V range and a 40V range without any overlap between them.
Inside one brand: what actually is compatible
For a single brand and a single platform, the rule is reversed and compatibility becomes very generous.
| Brand | The rule inside the platform |
|---|---|
| DeWalt | Every 20V MAX battery fits every 20V MAX tool, and FLEXVOLT packs run 20V tools in 20V mode |
| Ryobi | ONE+ packs fit every ONE+ tool made since 1996, lithium and old NiCad tools alike |
| Milwaukee | Every M18 battery fits every M18 tool and charger |
| Makita | Switched mounts entirely when lithium arrived, so old NiCad-era packs don't fit modern LXT tools |
The history of the situation is important since it affects the performance of older tools. The old 18V stem tools made by DeWalt can be used with modern 20V MAX battery packs via DeWalt's official DCA1820 adapter, which is the only instance in which a manufacturer has supported such an adapter. Ryobi has used the same stem for thirty years, which is the reason why a drill from the 1990s is still compatible with a new lithium battery. As for Makita and Milwaukee, both companies have designed their tools from scratch with new mounts.
For the deep dives: our Milwaukee M18 battery guide covers tiers and sizes, and the Ryobi battery guide explains ONE+ versus 40V.
The adapter question
Third-party adapters are needed since the locks exist; they are plastic connectors which allow a case from one brand to fit onto a tool from another brand, and they are sold in thousands.
What an adapter really does is to connect the power contacts and omit all the rest of the features. This includes the temperature monitoring, the low-voltage cutoff, and the handshake between the tool and the pack; the pack is unable to tell the tool to pull back when it gets hot, and the tool cannot tell the pack to switch off before the battery is drained too much.
And here's what the brands say, in their own words:
| Who | Their position |
|---|---|
| Makita | Batteries are not intended for, or authorized to be used with, any other brand's tools. Use with adapters or modified devices is excluded from warranty and repair coverage |
| Metabo HPT | So-called adapters are not tested or approved, and non-original batteries can't meet OSHA or UL listing requirements for workplaces |
The straightforward answer is that using an adapter means giving up the safety feature you paid for along with the warranty. The only adapter worth mentioning is the official one, DeWalt's DCA1820, which is intended for use with its own older tools. All the others go beyond the line that the manufacturers have set, and it's you who then have to bear the risk.
The one label exception: 18V vs 20V MAX
Now that we're dealing with myths, let me point out a label which appears to indicate incompatibility but doesn't. The official DeWalt website states that 20V MAX refers to a 20-volt peak figure for the same 18-volt nominal battery pack. Batteries of 18 volts and those of 20V MAX belong to the same category. If an entry lists both names, that's not a scam; it's just two names for the same item.
The 30-second compatibility check
Before you order anything, run this on the pack you're eyeing:
- The shape. Slide for slide, post for post. Compare photos from the same angle.
- The platform name. M18, ONE+, 20V MAX, LXT. The brand name alone is not the platform.
- The voltage class. 12V, 18V or 20V MAX, 40V. Same class, or walk away.
Thirty seconds, three checks, and most compatibility mistakes die right there. Once the three checks pass, you can browse replacement batteries by brand and pick the pack that matches. The full selection workflow, from finding the model number to screening the seller, is in our guide on how to choose a replacement power tool battery.
Common questions about battery compatibility
Are power tool batteries interchangeable between brands?
No. Each brand locks its packs to its own tools twice: once with the physical connector shape, and once with proprietary control circuitry. Within one brand and one platform, packs are interchangeable. Across brands, they are not.
Can you use a battery adapter to mix brands?
Physically, sometimes. Safely, almost never. Third-party adapters connect the power contacts while dropping the temperature monitoring, the low-voltage cutoff, and the tool-to-pack communication, and the brands exclude adapter use from warranty and liability coverage.
Is 20V MAX the same as 18V?
Yes. 20V MAX is the peak measurement with no load, and 18 volts is the nominal voltage of the same pack. Treat them as one class when you shop.
Are all DeWalt 20V MAX batteries compatible?
Yes, within the platform. Every 20V MAX battery fits every 20V MAX tool, and FLEXVOLT packs run 20V tools in 20V mode.
Do battery adapters void the warranty?
Yes. Makita excludes batteries used with adapters or modified devices from warranty and repair coverage, and Metabo HPT states that adapters are not tested or approved. Using one puts the liability on you.
Compatibility isn't anything mysterious; it's a matter of design. The shape keeps the wrong packs out, the chip keeps the wrong brands out, and the platform name shows you which ones are actually permitted in. If you match the shape, match the platform, and match the voltage class, the pack will fit as if it belongs, because it does.
References & Sources
- Power Tool Institute battery safety guidance (Power Tool Institute, the power tool industry's safety association)
- Makita official safety statement (battery use with other brands, adapters, and warranty exclusion)
- Metabo HPT warranty statement (adapter and non-original battery policy)
- DeWalt official site (20V MAX platform, FLEXVOLT 20V mode, DCA1820 adapter, nominal voltage footnote)
- Ryobi support (ONE+ platform compatibility since 1996)
- Milwaukee official site (M18 battery and tool compatibility)
Need a replacement?
When you're looking for a platform, you can browse for replacement batteries by brand. Since we carry compatible battery packs for twelve platforms, both the shape and the chip have already been taken care of, and if you have any questions you can ask them through our contact page.