Apple today published a support document warning customers against using uncertified Apple Watch chargers, which can cause slow charging, repeated calls, and decreased battery life.

According to Apple, customers should only use chargers made by Apple or chargers with Made for iPhone (MFi) certification and the Made for Apple Watch badge.

Apple provides images of original Apple Watch chargers and describes text and regulatory markings that may appear on the cable. “Non-Apple chargers may have different colors, text, or other graphics on the surface of the charging connector,” the support document states.

Apple also provides a list of the model numbers of all the cables it has released to date and provides instructions for checking the charger’s manufacturer using a Mac.

To use this method, you need to connect your Apple Watch to your Mac. Once connected, go to System Preferences and then click General. Select About and then System Report. Under USB, select Apple Watch Charger to view details. Watch chargers manufactured by Apple will indicate Apple Inc. as a manufacturer.

Apple says customers can make sure they’re using a certified third-party charger by looking for the Made for Watch label or by searching Apple’s public database of MFi accessories.