Can You Charge a Battery Through a Tool Adapter?
No. Cross-brand adapters only route power from the battery to the tool; they do not create the two-way communication a lithium pack needs to charge safely.
A tool adapter bridges two incompatible battery mounts so you can run a tool on a pack from a different brand. Many people ask whether they can also charge the battery through the adapter. The answer is no, and the reason is rooted in how lithium-ion packs are engineered to charge safely.
When you plug a battery into a charger, the charger and the pack’s internal electronics have a conversation. The pack sends data about its temperature, voltage, and state of charge, and the charger responds by adjusting current and stopping when the cells are full. This two-way communication prevents overcharging, overheating, and damage to the pack.
A tool adapter is a one-way bridge. It routes positive and negative power from the battery to the tool, and nothing else. There is no return path for charger commands to reach the pack’s management system. Forcing one would require the adapter to contain charger logic and charging connectors that simply are not there. Without that dialogue, a charger cannot safely charge a pack through the adapter.
The correct routine is simple: run the tool from the pack, then remove the pack from the adapter and place it on its own brand’s charger. The pack charges while the adapter sits unused.
Confusion point 1: USB charging ports on the adapter#
Some adapters include a small USB output port. This can create a false impression that the adapter charges things. In fact, the adapter is drawing power from the battery to charge a phone or small device. The power flow is FROM the pack, not TO it. The battery itself is not charging, it is discharging.
Confusion point 2: Within-brand manufacturer adapters#
DeWalt sells an official adapter called the DCA1820, which lets older 18V tools run on newer 20V MAX batteries. Because DeWalt made both ends, many users assume the adapter might handle charging as well. It does not. Even with manufacturer approval, the adapter is a tool-use bridge only. You still pull the pack off to charge it.
The same is true of any within-brand adapter. Compatibility usually means voltage alignment and mechanical fit for the tool mount. It never includes charging capabilities.
Why adapters cannot safely charge#
A lithium-ion pack contains a battery-management system (BMS), a small circuit board that monitors cell voltage, temperature, and current draw. When a charger is plugged in, the BMS and charger work together to regulate the charging process. If the pack overheats, the BMS tells the charger to stop. If one cell drifts out of balance with the others, the charger adjusts.
An adapter has no access to the BMS. It cannot read temperature or voltage or halt the charge if something goes wrong. Attempting to charge through an adapter would bypass these safety checks entirely, leaving the pack vulnerable to thermal runaway, cell damage, or fire.
The bottom line#
Every manufacturer designs adapters for tool use only. DeWalt does not expect you to charge through a DeWalt-to-Milwaukee adapter. Milwaukee does not expect you to charge through the reverse. No third-party adapter maker claims charging capability, and any listing that does is either wrong or a sign the seller does not understand the product.
The safe, simple, and correct method is to charge each pack on its own charger. This takes an extra 30 seconds and carries no risk.
Frequently asked questions#
Q: Can I charge a battery through a universal adapter? No. No adapter, third-party or manufacturer, supports charging. Even adapters marketed as “universal” are tool-use only.
Q: If I leave a pack in the adapter and plug the adapter into a charger, will it charge? No. The charger is designed to mate with the battery’s own charging connector, which the adapter does not provide. The tool mount and the charging mount are entirely different interfaces.
Q: Is it dangerous to try charging through an adapter? Yes. Without the BMS dialogue, a charger cannot regulate the charging process. The pack could overheat or overcharge, damaging the cells or creating a fire risk.
Q: Can I charge the battery while it is mounted on the tool via the adapter? No. The tool is not a charger. The tool draws current from the battery; it does not supply it.
Q: What should I do if my tool’s charger is broken? Buy a replacement charger for your battery platform. It is the only safe way to charge. For help finding adapters between batteries, see whether battery adapters are safe. For example, if you own DeWalt packs and want to run Milwaukee tools, review DeWalt battery to Milwaukee tool.