Is it safe to use car chargers with my new iPhone 7 plus?

No, car chargers are not bad for the battery. It is better to by one that is certified for the iPhone but the one you have should not damage your battery at all.

Hi

Subject to following Apple's guidance, car chargers are not harmful to iPhone. When using electronic accessories with your iPhone, Apple advises ensuring that they are either genuine Apple products or that they have been certified as Made for iPhone under the MFi program.

Certified items come with the "Made for iPhone" logo on them and/or on their packaging.

Using uncertified or counterfeit accessories may damage your iPhone and/or adversely affect operation. Apple's warranty does not cover damage caused by use with a third party product that does not meet Apple's specifications.

MFi-certified car chargers in the Apple Online Store in the US include:

Belkin car charger:

• http://www.apple.com/shop/product/HJ3H2ZM/A/belkin-car-charger-24a-12w

Belkin car charger with built-in Lightning cable:

• http://www.apple.com/shop/product/HJ3J2ZM/A/belkin-car-charger-24a-12w-with-buil t-in-lightning-cable

More information:

About iPhone, iPad, and iPod accessories - Apple Support