Milwaukee does not sell a standalone adapter that lets you snap an M12 battery onto an M18 tool, or the other way around. What Milwaukee does sell is a real, if unexpected, bridge between the two platforms, and it is built right into the product rather than sold as a separate accessory.
The bridge is the M12 heated jacket line. Milwaukee’s current M12 heated jacket listings describe the battery holder as “hidden in a sleek back pocket that expands for an XC battery” and note that “the pocket can be expanded further to fit any M18 battery pack.” In other words, if you already own M18 batteries for your drills, impact drivers, or other M18 tools, you can run a Milwaukee M12 heated jacket straight off an M18 pack without buying anything extra. That is a genuinely different design choice from a brand like DeWalt, which handles a similar internal bridge by selling a separate adapter accessory. Milwaukee just made the pocket bigger.
So is there an M12-to-M18 tool adapter?
No. For actual cordless power tools, Milwaukee does not offer an official adapter that crosses voltage platforms. You cannot put an M18 battery on an M12 drill, or run an M18 impact driver from a compact M12 battery, through any Milwaukee-made part. There is also no official Milwaukee-to-non-Milwaukee cross-brand adapter. If you see third-party adapters claiming to let a Milwaukee battery run a DeWalt, Makita, Ryobi, or Craftsman tool, those are not Milwaukee products and are not endorsed here.
The discontinued M18 Power Source
Milwaukee once made a related product called the M18 Power Source (49-24-2371). It was listed as “Compatible with M12 Heated Jackets with the Expandable Battery Pocket” and “Compatible with M18 Compact and XC Batteries,” and included a “Powered USB Port [that] Charges Portable Electronic Devices.” That wording made it sound like a useful companion for heated gear and mobile devices, but the product is now discontinued and no longer available for purchase. Do not plan a buying decision around it.
The practical charging bridge
Where Milwaukee does deliver practical cross-platform convenience is charging. The M18 & M12 Multi-Voltage Charger (48-59-1812) “Quickly charges all M12 and M18 Battery Packs” and “Accepts all M18 and M12 batteries, so you’ll always be prepared and productive, especially on jobs that require a mix of M12 and M18 Milwaukee cordless power tools.” If you work with both battery families, this is the one-plug answer. You do not need two chargers on the bench, and you do not need an adapter for charging purposes.
What about the M12 TOP-OFF?
Milwaukee also sells the M12 TOP-OFF Power Supply and Charger (48-59-1211). It “Fit’s All M12 Batteries” (Milwaukee’s own typo, quoted as published), includes a “15W Bi-directional USB-C Port To Charge Phones, Tablets, And Other Personal Devices,” and is “Compatible with all M12 Heated Gear.” It carries a 5-Year Warranty. This is not a cross-voltage adapter either, but it is worth mentioning because it is the current M12 side of Milwaukee’s power-source lineup: if your main concern is keeping an M12 jacket running or keeping a phone charged on site, this is the relevant product, not the discontinued M18 Power Source.
Bottom line
Milwaukee does not sell a tool adapter that lets an M12 tool run on an M18 battery or vice versa, and no official Milwaukee-to-non-Milwaukee cross-brand adapter exists either. But if you own M12 heated gear, you are not limited to carrying a spare M12 battery. The jacket’s own expandable pocket accepts a full-size M18 pack directly, which is a genuinely useful bit of cross-platform flexibility Milwaukee built into the product rather than selling separately. For actual tool use, the Multi-Voltage Charger (48-59-1812) is the practical answer if you are juggling both M12 and M18 tools day to day — one charger, either battery family, no adapter needed for charging purposes.
How this was checked
Facts on this page are drawn from Milwaukee’s own M18 Power Source, M12 heated jacket product listings, M18 & M12 Multi-Voltage Charger, and M12 TOP-OFF Power Supply and Charger product pages.
Sources checked: 2026-08-11. A new review date will only be set after the linked pages are re-checked.