Most cordless chargers refill a mid-size 18V-class pack in roughly 45 to 125 minutes, depending on the charger. A train horn gun uses so little energy per blast that charge time almost never decides whether you make it through a tailgate. What decides it is your plan: how many packs you bring, where the charger lives, and when you swap.
The short answer: charge time depends on the charger, not the horn
The horn doesn't charge anything. It's a bare tool that clicks onto a standard power-tool battery, so the pack comes off and goes on the charger from your battery platform, exactly as it would after a day of drilling. That means the honest answer to "how long does it take?" is whatever the charger's spec sheet says for your pack size. Here are the published numbers we could verify:
| Charger (battery platform) | Pack | Published charge time |
|---|---|---|
| DeWalt® DCB115 standard charger (20V MAX™) | 2.0Ah / 4.0Ah / 5.0Ah | About 30 / 60 / 70 min |
| DeWalt® DCB118 fan-cooled fast charger (20V MAX™) | 5.0Ah | About 50 min (retailer listing) |
| Milwaukee® M18™ Dual Bay Simultaneous Super Charger (48-59-1815) | FORGE™ XC6.0 | To 80% in about 15 min |
| Milwaukee® M18™ & M12™ Rapid Charger (48-59-1808) | Fully discharged packs | About 30 to 185 min, depending on pack |
| Bosch® GAL18V-20 compact charger (18V) | 4.0Ah | About 96 min to 80%, 123 min to full |
| Milwaukee® M18™/M12™ Vehicle Charger (48-59-1810), 12V outlet | 2.0Ah / 5.0Ah | About 45 / 125 min |
| DeWalt® DCB119 vehicle charger, 12V outlet | 1.5Ah / 3.0Ah | About 45 / 90 min |
Two patterns stand out. First, bigger packs take proportionally longer: on the same DCB115, a 5.0Ah pack takes more than twice as long as a 2.0Ah. Second, the charger's output matters as much as the pack. A 2-amp compact charger like the Bosch® GAL18V-20 needs about two hours for a 4.0Ah pack, while fan-cooled fast chargers cut that roughly in half. Times stretch further if the pack is hot or cold when it goes on, since the charger's electronics slow or pause charging until the cells are in a safe temperature range.
Why the first 80% is fast and the last 20% is slow
Lithium-ion chargers fill quickly at first, then taper the current as the pack nears full to protect the cells. You can see it in the Bosch® spec: about 96 minutes to reach 80% on a 4.0Ah pack, and another 27 minutes or so to finish the last fifth. Milwaukee® builds this into its Rapid Charger, which signals when a pack reaches 80% so you can grab it early.
For a horn gun, that 80% mark is the number to plan around. An 80% pack still has plenty of energy for a long session of horn use, and pulling it early can save half an hour or more when you're turning packs around between the parking lot and the stands.
How long one pack actually lasts on a horn gun
This is where horn guns differ from saws and grinders. The compressor only draws current while you hold the trigger, and the draw drops to essentially nothing when you let go. In our guide to blasts per battery charge, we estimate a 2.0Ah pack at roughly 400 to 600 short toots and a 5.0Ah pack at roughly 1,000 to 1,500. For long blasts of two to three seconds, plan on about a quarter of those numbers.
Put the two sets of numbers side by side and the math gets simple. A tailgate crowd that hits the horn on every first down and score might use a few dozen blasts in a game. Even an aggressive day is unlikely to empty a 5.0Ah pack, and a standard charger can refill that pack in about an hour. Charging is rarely the bottleneck. A dead pack usually means somebody forgot to charge it the night before.
The 5-Trumpet Horn Gun for Milwaukee® 18V Battery is a good example. It runs on any Milwaukee® M18™ battery you already own, puts out up to 150 dB through five metal trumpets, and comes with a remote that works from up to 160 ft away. Because it uses the same packs as your other M18™ tools, the spare in your toolbox is also your horn's backup.
The spare-pack plan for running all day
For a tailgate, game day, parade, or all-day event, the most reliable setup is two packs and one charger. You don't need a special battery. Any pack from your platform fits, so look in the garage first.
- Night before: Charge both packs to full. If one will sit for a week before the event, store it at mid-charge and top it up the evening before. Our charge-and-store guide explains why packs last longer that way.
- Pack A on the horn, pack B in the cooler bag: Keep the spare out of direct sun. Lithium-ion cells charge safely between roughly 32°F and 113°F, and a pack that bakes on a dashboard may refuse to charge until it cools.
- Swap on the fuel gauge, not on silence: When pack A drops to one bar, swap it. A low pack can make a horn sound weaker before it quits completely.
- Recharge pack A while pack B works: If you have shore power, a generator, or a 12V vehicle charger, put the drained pack on right away. On any of the chargers in the table above, it will be back to at least 80% long before pack B runs low.
- Bring a third pack for multi-day events: For a weekend festival or a two-day race with no outlet, three mid-size packs is a comfortable margin.
Charging in the truck: 12V vehicle chargers
If you're parked all day with no outlet nearby, a 12V vehicle charger lets you refill packs from the truck's power outlet. The tradeoff is speed. The Milwaukee® vehicle charger is listed at about 125 minutes for an M18™ 5.0Ah pack, compared with about 70 minutes for a 5.0Ah pack on the DeWalt® DCB115 wall charger. It's slower, but plenty fast for a horn that sips power.
Know these limits before you count on it:
- Some outlets switch off with the ignition. Milwaukee® notes that some vehicles cut power to the DC outlet when the engine is off. Check your truck before game day.
- Vehicle chargers protect the truck battery. The Milwaukee® unit is listed as shutting itself off to prevent excessive discharge of the vehicle battery, so it may stop partway through a charge.
- Heat slows everything. A charger and pack sitting in a closed cab in the sun can get hot enough that charging pauses. Keep them shaded and ventilated.
- Confirm the model is still sold. The DeWalt® DCB119 vehicle charger was discontinued in 2023, so look for a current model for your platform.
OSHA's lithium-ion battery safety guidance puts following the manufacturer's charging instructions first and names improper charging as a cause of battery fires. Use the charger made for your battery platform, and never charge a pack that is swollen, cracked, or has been soaked. You can read the guidance in OSHA Fact Sheet FS-4480.
FAQ
Can I charge the battery while it's still on the horn gun?
No. The horn gun has no charging port. Slide the pack off and put it on the charger from your battery platform, like any other cordless tool battery.
Does a fast charger hurt the battery?
A charger made for your platform talks to the pack's electronics and adjusts current to its temperature and charge level. For a horn gun pack that only goes through a few full cycles a year, charger speed has little effect on long-term wear. Heat and long-term storage at full charge matter much more.
Is a 2.0Ah pack enough for a full tailgate?
For most tailgates, yes. At roughly 400 to 600 short blasts per charge, a compact pack covers a typical game, and it charges in about 30 minutes on a standard DeWalt® charger. Bring a second pack if you lean on the horn for long blasts.
Should I wait for 100% before swapping back?
No. Grab the pack at 80% if you need it. The last 20% is the slowest part of the charge, and on a horn gun that last stretch adds runtime you probably won't use before the next swap.
For more on where to set up, how loud is too loud in a crowd, and which configuration works best in a stadium parking lot, see our guide to the best train horn gun for tailgating and sporting events.
