Charging my IWatch3 in the car and/or an external battery

Good afternoon Caballoblanco,

Welcome to the Apple Support Communities!

I understand you have some questions about how to safely charge your Apple Watch with an external battery or in your car. Here are a couple of examples from the Apple Store for products that have been approved to work with the Apple Watch. When considering other products, compare the charging information to what you see here:

Elevation Lab BatteryPro for iPhone and Apple Watch

"Integrated MFi-certified Apple Watch Magnetic charger

Smart high-speed USB out rapidly charges iPhone at 2.4A

Designed for comfortable carrying in your back pocket and when holding against the back of your iPhone (outside dimensions are close to those of an iPhone 7)

StowStrap flips to secure Apple Watch while charging, so you can charge in your bag or purse

8000 mAh battery provides more than two weeks of Apple Watch charges, three-plus days of iPhone use"

Belkin Car Charger (2.4A/12W) with Detachable Lightning Cable

"Single car charger

Full 5V/12W

2.4A for fast charging

Unique design

Detachable Lightning cable (4 ft./1.2 m) 

MFi certified

Take care.

The watch will not know the difference between the external charger and normal charging. Most cars trickle charge and charging would be so slow it would not be useful to use it. It is possible but not quick.

If you are using the Apple magnetic cable it will depend on the quality of the battery or 12v->USB power adapter to which it is connected. A socket built into your car will almost certainly be safe. A reputable brand device will almost certainly be safe. A cheap no-name or counterfeit adapter (or battery pack) which originated somewhere in Asia (but not necessarily where it says on the label) may be rather less safe, and you should consider your options for a hasty exit if it decides to emit smoke. Whatever you decide it is unlikely to harm your watch.

When did Community Specialists start competing against regular users?

I thought that you lot were for the OPs that don't get responses!