Oseyigut USB Thread Cable, Smart Wireless USB Charger Rechargeable Overcharge Protection for Adapter Devices with LED Indicators USB Electronic [ 2-Pack ]

Two small USB chargers with an LED status light and protection circuitry, for pen-style batteries. Output is DC 4.2 V at 420 mA from a DC 5 V input — a single-cell charge profile, which is what these are built for.

Specifications

• Input DC 5 V; output DC 4.2 V – 420 mA
• LED indicator: red while charging, green when full
• Protection circuitry: overvoltage, overcurrent, overcharge and short circuit, with charging stopped automatically once full
• Two per pack

Check the fit before you order — the listing does not specify a connector

Battery connectors are not standardised across pen-style devices: some thread on, some use a magnetic adapter, some are proprietary. The Amazon listing describes this only as plugging into a contact port and does not name a connector type or thread size, so confirm it against your own battery before buying rather than assuming. A charger that will not seat is useless however good the circuitry is.

The 4.2 V output is the useful clue: that is the full-charge voltage of a single lithium cell, which is what almost all pen-style batteries use.

Why two

This is the accessory people lose. Keeping a spare somewhere other than your pocket is the whole argument for the 2-pack.

On the protection circuit

The auto-stop matters more than it sounds. Leaving a small lithium cell on a dumb charger overnight is how batteries swell, and the cutoff is the difference between a charger you can forget about and one you have to watch.