Bizarre Things You Can Power With Milwaukee Batteries

You can power far more than drills and impact drivers with Milwaukee M18 and M12 batteries—think CPAP machines, mini fridges, soldering irons, and even electric scooters—but doing so usually voids warranties and risks damaging both the tool and the device. This article explains the most common (and weirdest) hacks, how the battery system works, what adapters you need, and why most of these projects are a bad idea unless you fully understand the electrical limits.

Formula

The core calculation for any battery-powered project is simple: Runtime (hours) = (Battery Voltage × Battery Capacity in Ah) ÷ Device Power Draw in Watts. In symbols: t = (V × Ah) / W. Here, V is the nominal battery voltage (18V for M18, 12V for M12), Ah is the amp-hour rating printed on the battery (e.g., 5.0 Ah), and W is the continuous power draw of the device you want to run. The result is an ideal runtime—real-world numbers will be lower due to inverter losses, voltage sag, and battery protection circuits cutting off before full discharge.

Worked Example

Using the default values from the calculator: an 18V M18 battery with 5.0 Ah capacity powering a 100W device. First, multiply voltage by amp-hours: 18 × 5 = 90 watt-hours. Then divide by the device draw: 90 ÷ 100 = 0.9 hours. That’s 54 minutes of ideal runtime. In practice, you’ll get closer to 40–45 minutes because the inverter or adapter wastes 10–20% as heat, and the battery’s protection circuit shuts down when voltage drops below ~14V, leaving some energy unused.

Background: Why Milwaukee Batteries Are Tempting

Milwaukee’s M18 and M12 battery systems are ubiquitous on job sites, and their high-capacity packs (up to 12.0 Ah for M18) store a surprising amount of energy. An M18 12.0 Ah battery holds 216 watt-hours—roughly the same as a small power station. The batteries also have built-in protection circuits that prevent overcurrent, over-temperature, and deep discharge, making them safer than bare lithium cells. That combination of capacity and safety features is why hobbyists and DIYers have found ways to tap into them for non-tool applications. The catch: Milwaukee designs these batteries to communicate with their own tools via a data pin. Third-party adapters often ignore that pin, which means the battery may not deliver its full rated current or may shut off under load.

How the Battery System Works

Milwaukee batteries use a standard slide-on interface with four main terminals: positive, negative, and two data/communication pins. The data pins let the battery and tool exchange information about temperature, voltage, and current limits. When you use an adapter to power a non-Milwaukee device, you typically only connect the positive and negative terminals. The battery’s internal protection circuit still monitors voltage and current, but without the tool’s controller, it may default to a lower current limit—often around 15–20 amps for M18 and 8–10 amps for M12. That’s plenty for many small appliances (a 100W device at 18V draws about 5.6A), but it means you can’t run high-draw devices like hair dryers or space heaters without tripping the protection circuit.

The Bizarre Things People Actually Power

Here are the most common (and genuinely odd) projects found on forums and YouTube, ranked roughly by practicality:

• CPAP machines – A 12V CPAP with a DC converter can run overnight on a 12.0 Ah M18 battery, though you’ll need a buck converter to step 18V down to 12V.
• Mini fridges – Small 12V cooler/fridges (40–60W) can run for several hours on a large M18 pack, but the compressor’s startup surge may exceed the battery’s current limit.
• Soldering irons – Portable USB-C soldering irons (like the TS100) can be powered directly from an M18 battery with a simple barrel jack adapter, giving hours of use.
• LED light strips – A buck converter to 12V or 5V lets you run LED strips for days on a single charge—one of the safest and most sensible hacks.
• Electric scooters – Some DIYers have wired M18 batteries in series to replace scooter batteries, but this is dangerous and requires a BMS that matches the scooter’s controller.
• Fish tank air pumps – A 12V air pump keeps running during power outages with an M18 battery and a voltage regulator.
• Amateur radio gear – Ham radio operators often use M18 batteries to power 12V transceivers, since the battery’s capacity is ideal for field operations.
• Electric blankets – Low-wattage 12V blankets can be powered for a night, but the current draw is high and may overheat the battery.

How to Choose an Adapter or Converter

If you’re determined to try one of these projects, the key is matching voltage and current. For M18 batteries (18V nominal), you need a buck converter to step down to 12V or 5V, depending on the device. For M12 batteries (12V nominal), a simple cable might work if the device accepts 12V, but check the device’s input range—many 12V devices tolerate 10–15V, but not 18V. When buying an adapter, look for one that includes the data pin pass-through (some third-party adapters claim to simulate the tool handshake, allowing higher current draw). Also, consider the battery’s discharge rate: a 5.0 Ah M18 battery can safely provide about 90W continuous (5A × 18V), while a 12.0 Ah pack can provide around 216W (12A × 18V). Exceeding these limits will trigger the battery’s overcurrent protection and shut it down.

Common Problems and Why You Probably Shouldn’t

The most common issue is the battery shutting off under load—especially with devices that have motors or compressors with high startup surges. Another problem is voltage mismatch: plugging an 18V battery directly into a 12V device can fry it instantly. Even with a converter, you’re bypassing the battery’s designed communication, which can lead to uneven cell discharge and reduced battery lifespan. There’s also a fire risk: if you use a cheap adapter without proper gauge wiring, it can overheat and melt. Finally, any modification voids the battery’s warranty and may be against Milwaukee’s terms of use. In short, these projects are fun engineering challenges, but they’re not reliable or safe for critical applications.

Safety and Alternatives

If you need portable power for a CPAP or a fridge, a dedicated power station (like a Jackery or EcoFlow) is safer, has proper voltage regulation, and includes multiple output ports. But if you’re set on using Milwaukee batteries, follow these rules: use a high-quality buck converter with current limiting, add a fuse or circuit breaker on the output, never leave the setup unattended, and check the battery temperature regularly. Also, never attempt to charge a Milwaukee battery with a non-Milwaukee charger—the pins are different and it’s a fire hazard. And if you’re building a multi-battery series setup, you must use a battery management system (BMS) to balance the packs—this is not a beginner project.

Frequently Asked Questions

Can I plug a Milwaukee battery directly into a 12V device? No. M18 batteries output 18V nominal (up to 20V when fully charged), which will likely damage a 12V device. You need a buck converter to step down to 12V.

How long will a 5.0 Ah M18 battery run a 100W device? About 54 minutes ideal, but expect 40–45 minutes in practice due to inverter losses and battery protection cutoffs.

Will using a third-party adapter damage my Milwaukee battery? Possibly. The battery’s protection circuit may not communicate properly, leading to overcurrent or over-discharge. It also voids the warranty.

Can I charge my phone with a Milwaukee battery? Yes, with a USB adapter that steps down to 5V. These are commonly available and safe, as long as you use a quality adapter.

Is it legal to modify Milwaukee batteries? Yes, for personal use, but it voids warranties and may violate safety certifications. Selling modified batteries is illegal in many jurisdictions.

What’s the maximum wattage I can draw from an M18 battery? It depends on the pack’s discharge rating. A typical 5.0 Ah pack can handle about 90W continuous, while a 12.0 Ah pack can handle around 216W. Exceeding that trips the protection circuit.

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in volt | Battery voltage | V | 18 | 0 | 120
in amp | Battery capacity | Ah | 5 | 0 | 20
in watt | Device power draw | W | 100 | 0 | 5000
out hours | Estimated runtime | h | (volt * amp) / watt | 2