SlotFree Open-Fit Magnetic Multi-Battery Tester with Self-Powered LCD Display

Saves money: Sorts good from bad, so you only replace what’s really empty.
Tired of wondering if the battery is dead… or the device is? The BT138 tells you in a second. and the screen shows the real voltage right away

No tiny slots—one open, easy-fit design
Many testers have a maze of small, size-specific slots. They’re hard to see, hard to line up, and easy to jam—especially with button cells. The BT138 replaces all those fiddly bays with a wide open base and a flexible strap. Lay any cell (AA, AAA, 18650, or button/coin) on the flat pad and swing the strap over—no hunting for the “right hole,” no forcing, no scratched labels. The large, flat contacts grab the battery ends instantly and give a clean reading without wobble.

Digital screen reading: Big, easy-to-read display shows the actual voltage (1.2V / 1.5V / 3.7V), so you know immediately if the battery is good, weak, or done.
No power required: The tester uses the battery you’re checking—no charging, no cords, always ready.
Supports multiple models: Household remotes, flashlights, toys, scales, power banks—test the cells they use.
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Saves Money & Reduces Waste
By testing before you toss, you’ll rescue usable batteries from the “dead pile,” replace only what’s actually empty, and recharge lithium cells at the right time. Fewer emergency runs, fewer half-used cells in the trash.

No tiny slots—easy, open fit
Most testers use small, size-specific bays that are hard to see and line up. BT138 has a wide open base and flexible strap: lay down AA/AAA/18650/button cells and secure—no hunting for the “right hole,” no jams, no scratched wrappers.

Polarity at a glance—no flip-and-retry
Big, high-contrast + / – marks show exactly where each end goes, and the strap naturally guides the positive to the top. You get a reading on the first try, even in low light.

Digital Screen Readout
A bright LCD on the head shows the actual voltage (e.g., 1.20V, 1.50V, 3.70V) the moment the battery touches the contacts. You can tell immediately whether a cell is strong, weak, or done—no color wheels or guesswork—so remotes, flashlights, toys, scales, and blood-pressure monitors get reliable power.

No Power Required
The tester uses the tiny energy from the battery being measured, so there are no cords, no charging, and no replacement cells to buy. It’s always ready when you pull it from a drawer, glove box, or tool bag.

Second-Speed Measurement
Touch the contacts and the reading stabilizes in about a second. That makes it easy to sort a whole box of mixed batteries quickly—keep the good, recharge the low lithium cells, and recycle the flat ones.

Supports Multiple Models
Designed for the sizes you actually use: AA, AAA (1.2/1.5V), 18650 Li-ion (3.7V), and button/coin cells commonly found in remotes, scales, watches, hearing-assist accessories, laser pointers, and key fobs. One compact tester covers the whole household.

Simple Clip + Flexible Strap
The springy red strap wraps the cell against the base while the top head touches the opposite terminal—easy to position with one hand. It holds short AAA and tall 18650 cells securely, so the display doesn’t flicker and you get a stable reading.

Clear Polarity Marks
Bold + / – symbols on the head and base help you line up the battery correctly the first time, protecting your devices and making the check effortless even in low light.

Compact & Portable
The BT138 is small enough for a pocket and light enough for a travel kit. Keep one in the kitchen drawer for remotes, one in the garage for tools, and one in the RV for flashlights—no more “is this battery good?” moments on the road.

Durable, Low-Maintenance Build
Rugged ABS shell, protected display window, and flush contacts resist wear. Wipe it clean—there’s nothing to calibrate or maintain.

SPECIFICATIONS