charging iPhone with third party chargers

That is correct - and the same also applies to car chargers.

MFi-certified car chargers in the Apple Online Store in the US, for example, 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

Hi

When using electronic accessories with your iPhone, ensure 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.

Genuine Apple Lightning to USB cables have certain text and a serial number printed on them.

Apple also recommends using the Apple USB Power Adapter that came with your iPhone (or another compatible Apple power adapter).

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.

More information:

About iPhone, iPad, and iPod accessories - Apple Support

Identify counterfeit or uncertified Lightning connector accessories - Apple Support

If you are concerned that damage may have occurred, then I suggest that you contact Apple Support (remote diagnostics and/or mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider to arrange for your iPhone to be checked and, if required, serviced:

iPhone Service Answer Center - Apple Support

For sure it would affect your battery life if it was a cheap charger and/or cable.

as a consequence, when your battery is negatively affected your iPhone might start restarting randomly and so this could affect its performance.

I recommend you spend little more money and get an original charger from an authorised apple store or reseller

Yes, that is OK.

The Apple Online Store details both the Mfr. Part Number and the UPC or EAN No. for each product (follow the links in my previous reply).

If you wish to purchase those same models elsewhere, then I suggest that you check that information with the seller.

do you refer to third party chargers within the MFI program? The whole point of the MFI program is to certify third party accessories. This should not occur.