The Milwaukee Tool has some very advanced battery technology and is available in two sizes: the Milwaukee M18 compact battery and the XC battery (extra capacity). But is there a difference? It turns out there is. Compared to typical 18V NiCd batteries, the M18 Li-Ion battery pack provides longer runtime and is 40% lighter. Both include Milwaukee's digital power management system to help ensure optimal battery life and runtime while protecting the battery and tool in demanding field applications. Let's face it, we've all abused our tools, so when Milwaukee built overload protection into the battery to prevent the tool from drawing too much current and burning out the motor or overloading the battery when being abused (*cough, hybrid thin group,* Cough) We know we've entered a new era of "smart" batteries.
Editor's Note: Check out our articles on Milwaukee battery warranties and Milwaukee RedLithium battery technology.
To illustrate how far we've come, note that each M18 Lithium-Ion battery is fitted with a temperature management system to keep the battery within an ideal temperature range and monitor individual cell voltages to help ensure optimal charging and discharge. It's these characteristics that help reassure consumers that these new batteries aren't just fake batteries with a one-year shelf life. In fact, the M18 battery has built-in discharge protection, which solves one of the main problems of NiCd and NiMH, preventing the battery from being damaged due to over-discharge.
Every M18 battery, including the Compact and XC models, has an integrated battery fuel gauge. This is a small membrane button that activates up to 4 LED lights on the front of the battery, telling the user the remaining runtime of the battery pack. If old NiCd was a reliable compass, then these Li-Ion batteries are the equivalent of a GPS.

Smart M18 compact battery?
With all this technology, it's no wonder we call these batteries "smart" batteries. Consumers will notice that the compact battery actually has an extra raised molded detent (whereas the XC only has one), rather than using a fully universal shoe connection for all Li-ion batteries. This actually prevents the Compact battery from being inserted into an incompatible tool.
For example, this means that you cannot plug a Compact battery into the M18 SawZall. This is done to protect the user from damaging the tool by overworking the motor to compensate for the lack of power, plus it ensures a better user experience (can you imagine powering a power-hungry cordless tool at half capacity?).
This physical battery barrier along with 5 electrical connection points (uncommon for DC powered devices) uses electronics and sensors so that a hybrid battery tool (like a hammer) can know which battery is inside and adjust torque accordingly.
Fully compatible with Milwaukee M18 tools
Per Milwaukee, the M18 compact battery (48-11-1815) will only work with the following tools (expect this list to grow as the company adds more tools):
- 2601 – Cordless Drill/Driver
- 2602 – Cordless Hammer Drill/Driver
- 2632 – Wireless ProPEX Extension Tool
- 2650 – Cordless 1/4″ Hex Compact Impact Driver
- 2651 – Cordless 3/8″ Compact Impact Wrench
- 2652 – Cordless 1/2″ Compact Impact Wrench
- 2625 – Hackzall Cordless One-Handed Reciprocating Saw
- 2790 – Construction Site Radio
- 0880 – Cordless Wet and Dry Vacuum Cleaner
- 2735 – LED Work Light
- 2710 – AC/DC Wall and Vehicle Charger
- 49-24-0171 – Cordless Work Light
- 48-59-1801 – Li-Ion Battery Charger
However, each tool can run on an XC (48-11-1828) battery and get extra runtime (and sometimes extra torque, like Milwaukee's line of impact drills). In short, the differences matter, but the overall execution and concept is pretty cool, showing that Milwaukee Tool has some really smart tools and batteries.