iPhone 6(S)/Plus 6s battery goes from 100% to 1% in minutes, condition 84%?

[OSXphoto]

Hi all, like the title says: 6s battery goes from 100% to 1% in minutes. So the battery needs replacement. But the system settings / battery / battery health shows 84%. Howzat?
This iPhone was purchased as refurb so I can't tell if the battery is original.

Safety?
This iphone is scheduled for replacement in may 2022 (7 months from now). Is it considered safe to keep using it, with a powerbank tied to it to last throughout the day? Or can the battery explode / release toxic gasses?

Thanks!

 

[mtneer]

Is the battery starting to expand? If not then get the battery service replacement until you can get a new device…

 

[Tmacc47]

I'd pay the money to get a new battery. My 6s battery health is at 93 percent and it's awful!

 

[now i see it]

If the front glass isn’t being pressed off and bulging up, the battery isn’t swelling. Swelling is usually caused by over charging.
Just because a lithium ion battery can’t hold charge like it used to doesn’t necessarily mean it’s hazardous use.

 

[that be me]

Sounds like something might not be connected right. A new battery could solve it if it's installed right, as well as improve that capacity.

 

[BigMcGuire]

The 6s had those batches of bad batteries. My wife's iPhone did this. Apple should replace it?

 

[ian87w]

Since it was bought refurb by 3rd party, I'd assume it's just a bad 3rd party battery. Best bet is to just replace the battery, and a trusty shop will be able to tell you if it has a genuine battery or not.

Using a phone tied to a powerbank is possible, but do you really want to do that? It defeats having a portable phone to begin with (unless you have those battery cases). If you really must use the phone for another 7 months, just replace the battery. Many 3rd parties can do it as parts for these older iPhones are aplenty.

 

[OSXphoto]

Thanks to you all for your input! Certainly no sings of swelling. Also: I figured since the "battery health" actually gives a reading, it should be still the original OEM Apple battery, but not sure if this assumption holds true.

We just found a family member that is interested to take the phone off our hands next year, so I'm taking the device to our local phone shop to get a new battery.

 

[OSXphoto]

For anyone interested: this is the battery that emerged from the iPhone 6s. It appears to be Apple original, date stamped 2013. Quite peculiar as this model was announced in 2015.