Fi Series 3+ vs Fi Mini: What’s the Difference & Which Should You Buy?

Last Updated on June 3, 2026 by Kieran Beckles

Are you ready to buy a Fi smart collar but can’t decide between the Fi Series 3+ and the Mini? I tested both devices on my Alaskan Klee Kai dogs, and in this comparison article, I’ll compare the size and fit, durability, GPS tracking performance, battery life, and my verdict.

I’ve used the Fi Series 3 for the past two years on Copper and Skye, but I got an updated Series 3+ and the Mini in 2026, to see which best served my needs and which GPS dog collar offered better value.

The Fi Series 3+ is more durable and better suited to medium- to large-sized dogs that like to be outside exploring, whether that’s in a large yard or on hikes. The device is integrated into the collar with a secure locking mechanism.

The Mini is ideal for sensitive dogs like Skye who don’t like bulky or heavy collars. I was able to attach the device to her existing collar.

When deciding between the Mini and Series 3+, network coverage is worth checking before buying either collar. However, if both AT&T and Verizon work well where you live, I’d make my decision based primarily on your dog’s size and comfort.

In this comparison article, I’ll be taking a close look at both Fi GPS dog collars to help pet owners make a decision and share my experience after testing with Copper and Skye.

Fi Series 3+ Vs Mini: Quick-fire Comparison

Testing Fi Series 3+ And Fi Mini On My Dogs

If you’re familiar with Life With Klee Kai, you’ll know that I invested in Fi Series GPS collars after a scary experience with Copper.

He slipped his previous collar and chased a coyote up a hill one morning on a walk. Fortunately, he returned unscathed. I immediately invested in Fi collars.

Copper and Skye have been using Fi Series 3 collars for the past three years, apart from when we’re filming content. So we’ve used it for quite some time.

Do you want to learn more about Series 3+?
Read more here.

However, Skye is a sensitive dog, and I was interested in trying the Fi Mini after Fi released its latest offering in 2025. I liked how lightweight it was.

I picked up a Fi Series 3+ collar for Copper to ensure both devices were brand new, in the same condition and the same starting battery life.

So we’ve tested both dog collars side by side for the past two months as part of our everyday lives. Whether that’s going for a walk, a hike, or just filming!

Fi Series 3+ Vs Mini: Key Differences At A Glance

Size & Fit

The Mini weighs 16 grams, while the Series 3+ weighs 47 grams. The Series 3+ dimensions are 81.5mm x 30mm x 11.5mm, while the Mini’s dimensions are 42mm x 30mm x 12.5mm. As you can see, the Mini is significantly lighter and slimmer.

The Fi Series Mini uses a silicone sleeve so you can attach it to your dog’s existing collar. This was perfect for Skye, who prefers lighter collars.

I didn’t have any problems placing the Mini inside the silicone sleeve and sliding the sleeve onto her collar. So from a fit perspective, it was ideal.

I like that the Mini gives you the flexibility to transfer the device to a different collar, should you decide to invest in a new one in the future.

The Mini looks proportionate in size to Skye – it’s not bulky or an eyesore on her neck. It’s perfect if you don’t want to overwhelm your small dog.

Copper’s Fi Series 3+ took slightly longer to assemble. I had to slide the Series 3+ device into the in-line collar and lock it in position.

Once I had the collar on Copper’s neck, I had to readjust it to fit snugly, but not too loosely. I’m perpetually paranoid after my previous experience.

The fit was good – I’d still like it a little more snug, but I did my best to adjust it as best I could! It has a much wider collar than the Fi Mini.

For that reason, I’d say it’s more suited to a medium or large dog than a toy-sized Alaskan Klee Kai dog.

Verdict: Fi Mini because it's slimmer and weighs less.

Cellular Network

I’ve tested these two Fi devices over the past two months and haven’t experienced any issues with tracking or coverage.

The Fi collars use multiple technologies together: GPS satellites determine your dog’s location, and the LTE-M cellular signal sends that location to your phone via Fi’s cellular network.

This is important to mention because the two devices use different cellular networks. The Fi Series3+ uses AT&T, and the Fi Mini uses Verizon.

If either of these networks has poor coverage in your area, it may impact your decision when deciding between these two collars.

That’s not an issue where I live. Thankfully, Fi doesn’t use the T-Mobile network, or I’d be in trouble. But I haven’t experienced any network issues.

We live in an urban area with some hills and trees, but coverage didn’t drop.

So I would say an important factor in your decision to buy either the Series 3+ or Mini would be the network coverage.

Verdict: I'd call this a tie because it's dependent on your area.

GPS Tracking Performance

Honestly, I didn’t notice any discernible difference in GPS tracking performance between the Series 3+ and the Mini.

The Fi Series 3+ has been reliable over the past three years, and the same was true with Copper’s new device.

I was interested to see if there would be a noticeable lag with the Fi Mini, but I really didn’t spot any difference.

Both devices tracked Copper and Skye’s activity and location without any issues, which was great because I wasn’t sure how the Mini would perform.

Because the Mini is part of the larger Fi ecosystem, it gets the same benefits as the larger Series 3+. That played out in my testing.

I did some research online because I was curious to learn about the experiences of other dog owners. My testing experience mirrored the online reviews.

Verdict: With little difference in GPS tracking performance, this is another tie.

Battery life

The Fi Series 3+ box includes the Fi base charger, which results in longer battery life, potentially lasting up to three months.

The Mini doesn’t include a Fi base charger and can be charged using USB-C. Its battery life is much shorter, up to six weeks, when using this method.

However, when the Mini is charged using the Fi base charger, it can match the Series 3+ battery life of three months. In that case, there’s no difference.

When you’re at home, the Series 3+ and Mini rely on Wifi and Bluetooth. There’s less strain on battery life, allowing the collars to run longer.

But if you travel a lot, you may notice the Mini lasts longer than the Series 3+. I found the Series 3+ loses charge quick as it searches for an LTE connection.

For instance, I checked my Fi app today, and you can see that my Mini still has 80% charge, but my Series 3+ only has 69% charge (pictured above).

Verdict: In my experience testing these two devices, I found the Mini had a better battery life.

Durability

The Fi Series 3+ and Fi Mini are both waterproof, which isn’t really a concern for us living in California, but good to know.

It is worth noting that the Series 3+ has a nightlight, but the Mini doesn’t. That’s one difference between these two devices.

I’ve used the Series 3+ for two years before introducing the Mini to Skye. The original Fi collars held up well during that time.

So I know that the Fi Series 3+ is a durable device based on my real-life experience using it with my Klee Kai.

I’ve only been testing the Mini for two months, but so far, I’m impressed. It shows no signs of wear.

Neither Copper nor Skye pulls a lot on the leash or is particularly destructive. So this wasn’t a concern for us.

But I could see why the Series 3+ might be considered more durable with its integrated design. The magnetic clasps ensure security.

Verdict: My dogs aren't particularly adventurous or destructive, but if your pets are, I'd go for Series 3+.

Price

There’s no difference in price. When you purchase either the Fi Series 3+ or the Fi Mini, you get the hardware for free.

You can read my in-depth article on Fi price here.

Instead, you’re paying for a Fi membership. This doesn’t fluctuate depending on the collar. It’s the same for the Series 3+ and the Mini.

Regardless of the device you choose, you’ll need to pay a one-time activation fee of $20. You get a one-year warranty included.

The Series 3+ comes in four colors (blue, yellow, grey and pink) and five sizes (extra-small, small, medium, large, and extra-large).

It’s worth noting that because the Series 3+ device is integrated into the collar design, you can only change the collar color by purchasing from specific companies.

It’s simple with the Mini device. There are no different colors or sizes because you’re attaching it to an existing collar.

Verdict: It's a tie with no difference in price. You're paying for the membership.

App and health features

I used the same app during testing and there’s no difference in the health features.

Fi monitored Copper and Skye’s health across the same categories: rest, activity, barking, eating, drinking, licking and scratching.

While the Fi app trackings location, it doesn’t have the same containment features as SpotOn or Halo.

How does Fi compare to SpotOn?
Find out here.

So if Copper or Skye were to wander off, it wouldn’t prevent them from doing so, but I would be able to use the Fi app to see their live location.

That’s something to keep in mind if you’re deciding between Fi and another smart dog collar brand.

Verdict: I didn't notice any differences in the app and health feature so it's a draw here.

Which Dogs Should Buy The Fi Mini?

• Dogs that weigh under 30lbs
• Dogs that are sensitive to weight
• Small or toy breeds
• Puppies
• Pet owners who travel a lot
• Dog parents who don’t want a bulky option
• People who don’t want to rely on the Fi charging base
• Dogs with narrow necks

Which Dogs Should Buy The Fi Series 3+?

• Dogs who weight over 30lbs
• Medium, large or extra-large breeds
• Pet parents who prefer an integrated collar design
• Dogs that like to explore
• Destructive dogs
• Dogs with thicker necks
• Dog owners who spend most of their time at home

Fi Series 3+ vs Fi Mini: My verdict

If I were to go back and buy one of these models for my two Alaskan Klee Kai dogs again, it would be the Fi Mini.

My Klee Kai weigh 15lbs each, and they’re quite sensitive dogs who don’t like heavy collars around their necks.

That’s why we’ve never stuck with brands such as Halo or SpotOn, because the collars were too bulky for Copper and Skye.

I love being able to attach the Fi Mini to their existing collars, which makes it easy to remove and put back on before and after filming.

I didn’t notice any difference in performance in the features that really mattered to me: live tracking, GPS location and activity monitoring.

We don’t manage to go on as many hikes as we used to with Copper and Skye. For that reason, I wasn’t worried about durability.

That said, the Fi Mini has held up well on Skye’s neck. I haven’t noticed any issues or wear.

There’s no price difference, and since I already have a Fi base charger, I didn’t need to worry about battery life.

If you’ve got a small or extra small dog, I’d recommend the Fi Mini. But if your dog is larger and you’re concerned about durability, the Series 3+ could be a better fit.

Fi Series 3+ vs Fi Mini FAQ

Wrapping up

We’ve reached the end of our Fi Series 3+ vs Fi Mini comparison article.

I’d recommend the Fi Mini if you’ve got a toy, small, or even a smallish medium dog. It’s lightweight and versatile.

Even if you have a medium- or large-breed dog, you may prefer the Fi Mini because it can attach to any dog collar.

However, the Fi Series 3+ is still a great option if you want an integrated dog collar and your dog doesn’t mind the extra weight.

My Alaskan Klee Kai dogs did appear more comfortable with the Fi Mini, especially since Skye is a small, sensitive dog.

Fi collars or Tractive?
I compare them here.

The other factor to consider when making a decision is network coverage ifv either AT&T or Verizon have poor coverage in your area.

If they both work well where you live like in our case, I’d make my decision based primarily on your dog’s size and comfort.