Hello Carmela, has your phone's software been updated in the last year? If so then there will be a feature in the settings menu called battery health. This section will tell you the “battery lifetime" which will display as 1-100% battery condition compared to a brand new battery. Think of your battery as a gas tank, but a tank that gets smaller every time it's filled. At 80% lifetime, your “gas tank” holds only 80% of the fuel it did when it was brand new. Apple will recommend a new battery once the lifetime shows below 80%. In my experience, I think it's worth the time and money to change your battery if it shows as anything below 86%. 85% is the point where most of my customers start complaining about unsatisfactory performance. A local independent repair shop can replace your battery in under 30 minutes and a reputable shop should give you 3 months-1 year warranty on that battery. An Apple store can replace your battery in a few hours, if you made an appointment before going in. If you are comfortable using small tools you can also replace the battery yourself. The iPhone 6s is one of the easier DIY battery jobs. If you plan to do it yourself I highly recommend ifixit's batteries. I have found no battery suppliers that are better than Ifixit, but I have used dozens that are worse.