If you already own a Milwaukee M18 or a DeWalt 20V MAX battery, you can run a portable train horn gun off the same pack you charge for your tools. The question shoppers ask most is simple: which battery system gives you more blasts before you have to swap packs? Here is the straight answer, with real numbers and no marketing fog.
The short answer
Neither brand is automatically "louder" or "longer-lasting" because of its name on the label. How many blasts you get is decided by the watt-hours stored in the specific pack you snap on, not by whether it says Milwaukee or DeWalt. A Milwaukee M18 5.0Ah and a DeWalt 20V MAX 5.0Ah hold the same energy, so they deliver essentially the same runtime on the same horn. If you want more blasts, the real lever is buying a higher-capacity pack within whichever system you already own.
"18V vs 20V" is a label, not a power difference
This trips up a lot of buyers. Milwaukee calls its system M18 (18 volts) and DeWalt calls its system 20V MAX, so it looks like DeWalt has more voltage to give. It does not. The 20V MAX number is the peak open-circuit voltage measured the instant before any current flows. The moment you pull the trigger and the horn's air pump draws power, a DeWalt 20V MAX pack settles to the same 18-volt nominal range that Milwaukee advertises up front.
Both systems are built from the same standard 18650 or 21700 lithium-ion cells. The difference is purely how each company chooses to print the voltage on the box: DeWalt uses the maximum, Milwaukee uses the nominal. Under load, the only condition that matters when your horn is blowing, they run at the same working voltage. So forget the headline number, it tells you nothing about blasts per charge.
How to compare blasts: think in watt-hours
Because both systems run at 18 volts nominal, the apples-to-apples way to compare energy is watt-hours (Wh), which is simply volts multiplied by amp-hours. More watt-hours means more total air pumped, which means more blasts before the pack dies. Here is how the common packs stack up.
| Battery pack | Working voltage | Amp-hours | Watt-hours |
|---|---|---|---|
| Milwaukee M18 XC 5.0Ah | 18V nominal | 5.0 Ah | 90 Wh |
| Milwaukee M18 HIGH OUTPUT HD12.0 | 18V nominal | 12.0 Ah | 216 Wh |
| DeWalt 20V MAX DCB205 (5.0Ah) | 18V nominal (20V peak) | 5.0 Ah | 90 Wh |
| DeWalt 20V MAX DCB609 (9.0Ah) | 18V nominal (20V peak) | 9.0 Ah | 162 Wh |
The pattern is obvious once it is in front of you. A 5.0Ah pack from either brand holds 90 watt-hours and gives you the same number of blasts. Step up to a bigger pack and runtime climbs in lockstep with watt-hours: a 162 Wh DeWalt pack will roughly double the blasts of a 90 Wh pack, and a 216 Wh Milwaukee pack pushes that even further. Runtime scales with energy stored, not with the brand badge.
Milwaukee M18 vs DeWalt 20V MAX, pack for pack
Where the two systems genuinely differ is at the top of each lineup. On the Milwaukee side, the M18 HIGH OUTPUT HD12.0 packs 216 watt-hours across 15 lithium-ion cells, and it is the largest standard M18 pack you can buy. That is the most blasts-per-charge you will get out of an M18 horn gun without carrying spares.
On the DeWalt side, the highest-capacity standard 20V MAX pack is the DCB609 at 9.0Ah, which works out to about 162 watt-hours at 18 volts nominal. That is a lot of blasts, but it lands below Milwaukee's biggest standard pack. So if your goal is the absolute maximum runtime from a single battery and you have not bought into either platform yet, the M18 ecosystem edges ahead at the top end. If you are comparing the everyday 4.0Ah and 5.0Ah packs most people actually own, the two systems are a dead heat.
Our 5-Trumpet Horn Gun for Milwaukee® 18V Battery is built to clamp straight onto your existing M18 packs, so the same battery that runs your impact driver runs your horn.
Prefer the yellow ecosystem? Our DeWalt horn guns slide onto the same 20V MAX packs in your truck box, no adapters and no rewiring.
Which system should you actually pick?
For the vast majority of buyers the decision is already made: buy the horn gun that matches the batteries you own. If your garage is full of red Milwaukee packs, an M18 horn gun means zero extra batteries and chargers to buy. If you run DeWalt for everything else, stay yellow. The cost and hassle of starting a second battery platform almost always outweighs the modest top-end runtime advantage of one brand over the other.
Only if you own neither system, and you specifically want the longest single-pack runtime, does the M18 lineup's bigger top pack become a tiebreaker. For everyone else, blasts per charge comes down to the capacity of the pack you grab, not the logo on it.
How to get more blasts out of any pack
- Carry the biggest pack you own. Watt-hours are everything. A 5.0Ah or larger pack will outlast a compact 2.0Ah several times over.
- Keep a charged spare in the truck. A second pack is the cheapest way to effectively double your runtime in the field.
- Store batteries at room temperature. Lithium-ion packs lose usable capacity in extreme cold, so a freezing pack delivers fewer blasts than the same pack at 70°F.
- Top off before a trip. Self-discharge is slow, but a pack left for months will not give you its full rated runtime until recharged.
FAQ
Does a DeWalt 20V MAX battery really give the same blasts as a Milwaukee M18?
At the same amp-hour rating, yes. Both run at 18 volts nominal under load and a 5.0Ah pack of either brand stores 90 watt-hours, so the horn behaves the same on either system. The brand name does not change how much air gets pumped.
Will a higher-voltage battery make my horn louder?
No. Loudness comes from the horn's trumpets and air pump design, not from a couple of marketing volts on the label. A bigger battery gives you more blasts, not a louder blast. To go louder you change the horn configuration, not the pack.
Can I use a DeWalt FlexVolt battery on a 20V MAX horn gun?
FlexVolt packs are designed to step down and run 20V MAX tools, so they physically fit and power 20V MAX-style devices. Always confirm fit with your specific horn gun before relying on it, since FlexVolt packs are larger and heavier than standard 20V MAX packs.
What is the most blasts I can get from one battery?
Buy the highest-watt-hour pack in your system. On Milwaukee that is the M18 HD12.0 at 216 watt-hours; on DeWalt the standard top pack is the 9.0Ah at about 162 watt-hours. Runtime scales directly with those numbers.
Do I need an adapter to use my tool batteries on a horn gun?
No. Our horn guns are made for a specific battery footprint, so a Milwaukee horn takes M18 packs and a DeWalt horn takes 20V MAX packs directly. There is no adapter, no wiring, and no charging changes.