How long should my phone battery last?
Anyone tell me how long their phone lasts between having to charge? Mine is a hand-me-down iPhone 6s Plus, just saw in the 'About' section "There is an issue with your phone battery"

It drains from 100% to 10% in less than 20 minutes of use, & even when inactive it will often go all the way to 1% battery. My mom reckons they do it on purpose to compel people to buy new version. Is it built in obsolescence?
Also asked someone what her phone plan was, she told me $50 a month for unlimited internet usage. I looked it up from her provider and it was $55 a month for 250gb, not unlimited.

I'm wondering all this because I need a good battery life & data plan so i can use the map feature when navigating on the road.
We're in Australia so it's basically a choice between Telstra or Optus