Overview
The Yocan FLAT Series tackles one of the most annoying problems with pen-style 510 batteries: they roll everywhere. Set it on your desk, turn around, and it's on the floor. The FLAT Series fixes this with a square profile that stays put.
What We Tested
Our hands-on testing methodology
Units Tested
FLAT Mini and Slim
Testing Period
9 days of use
Voltages Tested
2.6V, 3.2V, 3.8V
Cartridges Tested
6 different carts
Anti-Roll
Surface stability tested
Battery Life
350mAh and 400mAh
The series includes multiple variants. The FLAT Mini and FLAT Slim are the most compact options. Both have variable voltage, preheat mode, and USB-C charging. The main difference is size and battery capacity.
Design & Build Quality
The standout feature is obvious the moment you see it: the square cross-section. This isn't just a style choice. It's a practical fix to a real problem. Set it down on any surface and it won't roll away.
FLAT Slim vs FLAT Mini
| Feature | FLAT Slim | FLAT Mini |
|---|---|---|
| Battery Capacity | 350mAh | 400mAh |
| Dimensions | 12 x 12 x 84mm | 15 x 15 x 71mm |
| Weight | 0.77 oz | 0.95 oz |
| Form Factor | Taller, thinner | Shorter, wider |
The FLAT Slim is more discreet. It's narrower and slides easily into pockets. The FLAT Mini, despite the name, actually has a slightly larger footprint but shorter height. It feels more substantial in hand.
Both models have a sturdy zinc-alloy frame with a rubberized coating for grip and durability. The construction feels premium for the price. Color options include Black, Silver, Blue Pink, Green White, Purple Pink, and Red Teal.
Features
Variable Voltage
The FLAT Series offers 3 voltage settings:
| Voltage | LED Color | Best For |
|---|---|---|
| 2.6V | White | Maximum flavor, delicate terpenes |
| 3.2V | Green | Balanced flavor and vapor production |
| 3.8V | Red | Maximum vapor, thick oils |
Click the power button 3 times to cycle through voltage settings. The LED color shows your current selection.
Preheat Function
The 10-second preheat function runs at 1.8V and gently warms your cartridge without burning the oil. This helps with:
- Cold weather use
- Thick or viscous oils
- Cartridges that have been sitting unused
- Getting the last drops out of your cart
Double-click the power button to activate preheat mode.
Safety Features
Yocan included the essential safety features:
- 15-second safety cutoff: Prevents overheating during extended draws
- 5-click on/off: Prevents accidental activation in pockets
- Resistance protection: Only works with cartridges >0.8 ohm
USB-C Charging
All FLAT Series batteries have USB-C charging. This is a welcome upgrade from older micro-USB designs. The smaller models reach full charge in under an hour.
Performance
Vapor Production
At 2.6V, the FLAT Series produces smooth, flavorful vapor that's great for terpene preservation. The middle 3.2V setting is a nice balance for everyday use. And 3.8V delivers satisfying clouds if you prefer more vapor.
The voltage range of 2.6V to 3.8V is a bit conservative compared to some competitors. But it covers the sweet spot for most 510 cartridges. You won't accidentally burn your oil or get wispy hits.
Battery Life
Battery life varies between models:
FLAT Slim (350mAh): Expect 100-150 puffs per charge. That's fine for light to moderate daily use. Power users will need to charge daily.
FLAT Mini (400mAh): You'll get around 120-180 puffs per charge. A bit more runway between charges while staying compact.
If battery life is your priority, check out the larger FLAT (650mAh) or FLAT Plus (900mAh) variants in the same series.
Cartridge Compatibility
The standard 510 threading works with virtually all oil cartridges on the market. The magnetic connection provides a secure fit without screwing cartridges in. The >0.8 ohm resistance requirement means the FLAT Series is built for oil cartridges, not low-resistance atomizers.
Pros & Cons
Pros:
- Square design prevents rolling, which is more useful than you'd think
- USB-C fast charging across all models
- Great value at under $20
- Multiple size options for different preferences
- Nice gradient color choices
- Solid build quality with zinc-alloy construction
Cons:
- Smaller models (Slim/Mini) have limited battery life for heavy users
- Voltage range is narrower than some competitors
- No digital display for precise voltage reading
- Only compatible with higher resistance cartridges (>0.8 ohm)
Verdict
The Yocan FLAT Series delivers what it promises: reliable, good-looking 510 batteries at a great price. The square design isn't a gimmick. It actually improves daily use by keeping your battery where you put it.
For most users, the FLAT Mini offers the best balance of portability and battery life. Go with the FLAT Slim if you need maximum discretion and don't mind charging more often.
At under $20, the FLAT Series is an easy recommendation for anyone looking for a dependable cartridge battery. Practical design, solid construction, and useful features make this a standout value. For more options, see our roundup of the best cheap 510 batteries.
Related: Yocan FLAT Series Manual | Yocan UNI Pro 2 Review