Quick answer, because that's why you're here: the standard wireless fob on a Train Horn for Milwaukee® 18v Battery runs on two CR2016 lithium coin cells, and the long-range fob runs on a common 9V battery. I've swapped both on my own remotes enough times to have opinions about it, so here's the full rundown — which cell goes where, why you can't cheat with a CR2032, how long a fresh set actually lasts, and the one safety rule I don't bend on.
The Quick Answer: Two CR2016s in the Standard Fob, One 9V in the Long-Range Fob
Every M18™-compatible train horn I test ships with a wireless remote, and the batteries come pre-installed — so out of the box you don't touch anything. But fobs ride around in pockets, glove boxes, and UTV cubbies, and eventually the battery is the thing that quits. Here's what each remote takes:
| Remote | Rated range | Battery | Voltage |
|---|---|---|---|
| Standard fob (included) | Up to 160 ft | Two CR2016 lithium coin cells | 3V each (6V stacked) |
| Long-range fob | Up to 2,000 ft | One 9V battery | 9V |
The CR2016 is about as common as coin cells get — it's a 20 mm diameter, 1.6 mm thick lithium cell, the same family that runs watches and car key fobs. Per Energizer's own datasheet, each cell is rated 3 volts nominal with roughly 100 mAh of capacity and an operating range from -30°C to 60°C (-22°F to 140°F). Any grocery store, pharmacy, or hardware store battery rack will have them. The 9V in the long-range unit is even easier — it's the same rectangular battery in your smoke detector.
My Extreme Quad Train Horn for Milwaukee® 18v Battery came with both remotes in the box — the standard fob for around-the-truck use and the long-range fob for when the horn is staged away from where I'm standing. That's the setup I've been running hardest, and both fobs are still on batteries I replaced once, casually, in two seasons of use.
Why Two CR2016s — and Why One CR2032 Won't Cut It
Here's the trap I want you to avoid, because I've watched a buddy fall straight into it. The CR2032 — the most common coin cell on earth — is the exact same 20 mm diameter as the CR2016 but twice as thick: 3.2 mm versus 1.6 mm. Which means a single CR2032 slides into the standard fob's battery well perfectly, because two stacked CR2016s add up to the same 3.2 mm height. It fits like it was made for it.
It wasn't. Two CR2016s stacked in series deliver about 6 volts. One CR2032 delivers 3 volts. Drop a CR2032 in there and the transmitter is running on half the voltage it was designed for — best case you get a weak, short-range signal; typical case the fob just acts dead and you start blaming the receiver. The reverse mistake is worse: never stack two coin cells in a device built for one, because doubling the voltage can cook the electronics. Match what came out of the fob, exactly.
One more buying tip from the diesel-shop years: coin cells self-discharge on the shelf — lithium cells like the CR2016 lose roughly 1% of capacity per year, which is excellent, but only if the cell hasn't already sat in a dusty blister pack since before your truck was built. Buy from a store that actually turns over its battery stock, and check the date code printed on the packaging. A "fresh" cell that's five years into its roughly 8-year shelf life is starting the race half-tired.
How to Swap the Batteries Without Wrecking the Fob
Neither swap needs anything more exotic than a small screwdriver. Here's my routine:
Standard fob (two CR2016s):
- Open the case — depending on the fob revision it's either a small screw on the back or a seam you gently pry with a plastic trim tool or a thumbnail. Work the seam evenly; don't crank on one corner.
- Before you tip the old cells out, look at the orientation. Photograph it with your phone if you want — that's what I do, because the stack goes back in the same way, positive sides facing the same direction as the cells you removed.
- Wipe the contacts with a clean, dry cloth or the tip of a pencil eraser. Any film or corrosion on those little spring contacts costs you range.
- Load two fresh CR2016s, snap or screw the case shut, and test-fire the horn from across the driveway before you call it done. (Warn the household first. Ask me how I know.)
Long-range fob (9V):
- Slide or unscrew the back cover, unclip the old 9V from the snap connector, clip on the new one. The connector only fits one way, so orientation takes care of itself.
- Seat the battery so it doesn't rattle — a loose 9V bouncing around a UTV cubby will eventually stress the snap contacts.
Total time for either job: under two minutes. If the remote still won't fire after a fresh battery, the battery was never the problem — jump down to the guides in the Keep Reading box, because at that point you're into pairing and receiver territory, not battery territory.
How Long the Batteries Last — and the First Symptom They're Dying
The good news about horn fobs: unlike a key fob that polls constantly, these transmitters only draw meaningful power when you actually press the button. Each press is a fraction-of-a-second radio burst. So the batteries mostly die of old age, not of use — shelf-life math matters more than press-count math. With the CR2016's roughly 1%-per-year self-discharge, I comfortably get multiple seasons out of the standard fob, and the 9V in the long-range fob carries several times the capacity of a coin cell (Energizer rates its 9V alkaline around 600 mAh, with a 5-year shelf life).
The first symptom of a dying fob battery is not a dead remote — it's shrinking range. A fob that used to trigger the horn from across the lot starts needing you within a few truck lengths, then a few feet, then nothing. If your working range is quietly collapsing, swap the battery before you touch anything else; in my experience that fixes most "remote problems" outright.
Cold makes everything worse, temporarily. Lithium coin cells are rated down to -30°C, but their voltage sags as the temperature drops, and alkaline 9Vs are only rated to about -18°C (0°F). A fob that lives in the truck overnight in a Midwest January will act weak at dawn and recover by lunch. Don't replace a battery at 6:00 AM in the cold and declare victory — test again warm.
One related note: the fob battery and the horn's main battery are separate conversations. The receiver module on the horn draws a small standby current from the M18 pack itself, which is why I pull the pack off the horn for long-term storage — I covered the measurements in my standby-drain writeup. The coin cells in the fob, though, can stay put; their self-discharge is negligible.
Coin Cell Safety: Kids, Pets, and Disposal
I'm not going to lecture, but I am going to say this once, clearly, because the numbers are ugly. A swallowed coin cell can burn through a child's esophagus in as little as two hours, and the CPSC counted 27 deaths and an estimated 54,300 emergency-room injuries tied to swallowed or inserted button and coin batteries from 2011 through 2021. That's why Reese's Law now requires child-resistant battery compartments and warning labels on consumer products that use these cells — the details are in the CPSC's announcement. My rules: spare cells live in their child-resistant packaging until the minute they go in the fob, dead cells never sit loose on the bench, and if a cell ever goes missing around kids, that's an emergency-room call, not a wait-and-see.
Disposal is easy to get right. The EPA says button and coin lithium cells should not go in household trash or curbside recycling — tape over the terminals (or bag each cell separately) and drop them at a battery recycling point; their used household batteries page explains the why and where. Same taping habit applies to dead 9Vs: those exposed twin terminals love to short against pocket keys and drawer junk.
FAQ
Can I use one CR2032 instead of two CR2016s?
No. It physically fits because two CR2016s stack to the same 3.2 mm height as one CR2032, but you'd be feeding a 6-volt circuit only 3 volts. The remote will be weak or dead. Use exactly what came out: two CR2016s.
Do the standard and long-range remotes take the same battery?
No — the standard fob (rated up to 160 ft) takes two CR2016 coin cells, and the long-range fob (rated up to 2,000 ft) takes one 9V. This is consistent across the lineup of train horns for the Milwaukee® 18v battery, so a couple of spare CR2016s and one spare 9V in the glove box covers you completely.
I put in fresh batteries and the remote still won't fire. Now what?
Then the battery was never the culprit. Next suspects, in order: the fob lost its pairing to the receiver, the receiver antenna is pinched or shielded by metal, or the main M18 pack on the horn is flat. I've written full step-by-step guides on pairing and on diagnosing a dead remote — both are linked in the Keep Reading box below.
Should I pull the fob batteries for winter storage?
Not necessary. Lithium coin cells self-discharge at roughly 1% per year, so they'll happily hibernate in the fob. The battery worth pulling for storage is the M18 pack on the horn itself, since the receiver draws standby power.
Do the remotes come with batteries installed?
Yes — every remote I've unboxed shipped with batteries pre-installed and ready to pair. The replacement question only comes up a season or two down the road, which is probably why you're reading this.
Loud is a feature — install it right. And keep two spare CR2016s in the console. — Cole
Milwaukee®, M18™, and other trademarks are the property of their respective owners. Our train horns are independent aftermarket products that run on Milwaukee® M18 batteries; they are not manufactured, sold, affiliated with, or endorsed by Milwaukee® Tool / Techtronic Industries. Trademarks are referenced solely to indicate battery compatibility.