Short answer up front: yes. If you own Bauer or Hercules tools from Harbor Freight, Hart tools from Walmart, or Kobalt tools from Lowe's, a train horn gun built for your battery mount runs off the same packs you already charge for your drill — no adapter, no separate horn battery, no wiring. These store-brand and value-brand systems are every bit as horn-ready as the name brands. Below is the per-brand breakdown, the one voltage quirk on the Kobalt line worth knowing, and why you buy the horn made for your specific mount.
The short answer: all four platforms drive the compressor
A train horn gun is just a tool that hangs off your battery. Inside the body is a small air compressor that spins up the instant you squeeze the trigger and stops the moment you let go. Any 18V-class slide-on pack that powers your drill or impact driver has more than enough current to drive that compressor. Bauer, Hercules, and Hart all use the same five-cell lithium-ion architecture as Milwaukee, DeWalt, and Ryobi, so a horn designed for their mount treats your battery exactly like the tool it shipped with. Kobalt's main cordless line runs a little higher — more on that below — but it powers a horn gun just the same.
The only real variable is the physical mount. Each brand uses its own rail-and-terminal shape, so you buy the horn gun built for the packs you already own. Get the right mount and the battery clicks on the same way it does on your saw. For the full lineup at a glance, our train horn battery compatibility chart by brand lays out every system side by side.
Bauer 20V (Harbor Freight): five cells, 18V nominal
Bauer's "20V Max" label trips people up, but the math is simple. The 20V figure is the peak voltage off the charger with no load on it; the nominal running voltage is 18V. That comes from five lithium-ion cells wired in series at 3.6V nominal each — the same arrangement behind every "18V" and "20V Max" battery on the market. A horn gun's compressor is tuned for exactly that window, so any Bauer HyperMax pack spins it to full pressure.
The Bauer 20V line is fully interchangeable across its own tools, and Harbor Freight sells the packs in 1.5Ah, 3.0Ah, and 5.0Ah capacities. Every one of them shares the same slide mechanism and terminals — the only difference is the amp-hour rating, which sets your run time. The compact 1.5Ah from a drill kit and the bigger 5.0Ah high-capacity pack both fire the same horn. You're not dedicating a battery to the horn; you grab whichever Bauer pack is charged.
Hercules 20V (Harbor Freight): the heavier-duty Harbor Freight line
Hercules is Harbor Freight's higher-tier cordless brand, and its 20V batteries follow the same rule: 20V peak off the charger, 18V nominal under load. Hercules packs are interchangeable across every Hercules 20V tool, and Harbor Freight offers them from roughly 2.0Ah up to 8.0Ah, with the Extreme-Performance packs built on larger 21700-format cells for more capacity. Any of them clicks onto a Hercules-mount horn and runs the compressor without strain.
One thing Hercules owners should not assume: a Hercules pack does not natively drop onto a Bauer-mount horn, and vice versa. Even though both are Harbor Freight 20V systems at 18V nominal, the mounts are shaped differently. Third-party adapters exist to cross them, but you don't need one — just pick the horn built for the mount you already use. If your shop is loaded with the bigger Hercules packs, that 8.0Ah battery will give you the most blasts per charge of any pack in this group.
Hart 20V (Walmart): one battery, every Hart tool
Hart's 20V system, sold at Walmart, is marketed as a "one battery" platform — meaning the same pack interchanges across all Hart 20V tools. Electrically it's the familiar five-cell, 18V-nominal lithium-ion design, with the "20V" referring to the off-charger peak. Hart sells the batteries in 1.5Ah, 2.0Ah, 4.0Ah, and 6.0Ah capacities, and they're all fade-free lithium-ion, so the horn gets steady voltage right down until the pack is nearly empty.
For a Hart owner that means the horn gun is just one more thing in the lineup. Slide on whatever Hart pack is topped off, squeeze the trigger, and the compressor runs. The 4.0Ah and 6.0Ah packs are the sweet spot if you want a long session of blasts between charges; the compact 1.5Ah still works fine for quick, occasional use.
Kobalt 24V Max (Lowe's): the one voltage you should double-check
Kobalt is the outlier in this group, and it's worth a careful read. Kobalt's flagship cordless line at Lowe's is "24V Max," not 20V. Those packs are built from six 18650 cells for a nominal voltage of about 21.6V, with the 24V figure being the off-charger peak. That's a notch above the 18V brands, but it's still well within what a horn-gun compressor handles — more headroom, not a problem. A Kobalt-mount horn is built for that 24V Max pack specifically.
The thing to watch is Kobalt's other voltages. Alongside 24V Max, Kobalt also sells 40V and 80V outdoor-power lines, and those are entirely separate systems — different mounts, different voltage, not interchangeable with 24V Max tools or each other. So when you match a horn to your Kobalt packs, confirm you're holding the 24V Max battery (the blue cordless-tool pack), not a 40V or 80V lawn battery. Kobalt 24V Max batteries are interchangeable across all Kobalt 24V Max tools, in capacities from 1.5Ah up to 8.0Ah, so any of those will run the horn.
One mount per brand: why you buy for your platform
The recurring theme across all four brands is the same one that governs the name-brand systems: the battery chemistry is interchangeable, but the mount is not. A Bauer pack won't natively click onto a Hercules horn, a Hart pack won't fit a Kobalt mount, and so on. That isn't a limitation of the horn — it's just how every cordless platform protects its own ecosystem. The fix is simple: choose the horn gun made for the brand of batteries already sitting on your charger.
If you happen to own packs from several of these brands, you don't have to pick a favorite — each platform has its own matching horn. And if you're cross-shopping against the big names, the same horn design is offered across every major mount. The loudest in the whole family is the 5-Trumpet Horn Gun for Milwaukee® 18V Battery; the Bauer, Hercules, Hart, and Kobalt versions use the same trumpet-and-compressor core, just with the mount swapped to fit your packs. Loudness comes from the trumpet count, not the battery brand. For the closest comparison to these value platforms, our guide to Craftsman V20, Bosch 18V, and Ridgid compatibility covers the other second-tier systems the same way.
FAQ
Is a Bauer or Hart "20V" battery too much voltage for the horn?
No. "20V Max" is the peak voltage off the charger; the nominal running voltage is 18V, the same as every other 18V-class pack. The horn's compressor is built for that range, so any Bauer or Hart 20V battery fires it without issue.
Will a Kobalt battery work even though it's 24V?
Yes, as long as it's a Kobalt 24V Max pack on a Kobalt-mount horn. The 24V Max line runs about 21.6V nominal — a bit above the 18V brands, which just gives the compressor a little extra headroom. Don't try to use a Kobalt 40V or 80V battery; those are separate systems with different mounts.
Can I use a Bauer battery on a Hercules horn, or mix brands?
Not natively. Even though Bauer and Hercules are both Harbor Freight 20V systems at 18V nominal, the mounts are shaped differently, so a pack from one won't click onto the other's horn. Buy the horn built for the brand of batteries you actually own.
Do I need to buy a special battery for any of these horns?
No. Each horn uses the same batteries you already own for that brand's tools. A larger amp-hour pack simply gives you more blasts per charge. You only buy the horn built for your platform's mount — the battery and charger are the ones you already have.
Which capacity gives the most blasts per charge?
The biggest amp-hour pack on your platform — an 8.0Ah Hercules or Kobalt, or a 6.0Ah Hart — holds the most energy and delivers the longest run of blasts. A compact 1.5Ah or 2.0Ah still works fine for quick, occasional use; it just empties sooner.