My phone was replaced already once bc of the battery now the battery is bad again is it covered

No. Batteries are consumables; they lose capacity every time they are discharged, then recharged. Apple will replace the battery for $49, but, as your phone is almost 8 years old, it might be time to consider replacing the phone with a newer model.

Blo52 wrote:

My IPhone 6 was replaced less then 2 yrs ago bc of the battery now this battery is bad will they replace it for free

Apple only has a 90 day warranty on replacement batteries or replacement devices - at least in the United States. Not sure what it is in other countries.

https://www.apple.com/legal/sales-support/terms/repair/retailservice.html

Apple warrants for a period of ninety (90) days from the date of service (1) that service will be performed in a competent and workmanlike manner and (2) that all parts used to service your product will be free from defects in materials and workmanship, unless otherwise specified by Apple. Apple further warrants to the extent permitted by law, that batteries installed as part of Apple’s battery replacement service for Apple portable Mac computers will be free from defects in materials and workmanship for one (1) year from the date of service.