Jeez that's terrible. We all know stuff will eventually break down but for the manufacturer to purposely nerf it really stinks.
@fidodie its pretty old, but you're thinking throttling? Probably not remotely worth changing the battery which does still hold up decently.
what @shrpshtr325 said. as the battery degrades, they throttle the processor to maintain battery life at the expense of performance.
They are supposed to put some sort of 'choice' selector in the battery section of settings if this is the case. think it went in IOS 11.
The engineers made this choice without disclosing it, and it was turned into "apple reduces performance so people would buy new equipment" -
it was just a choice to have a mobile device last while not near power - as it is useless if it is dead, as opposed to just slower.
i'll also note, the web pages and apps are getting more complicated, so they do take more power to run.
there is also the chance that shared libraries are out of date with the app, and causing problems. Could do a full reset, update, then reinstall apps you use.
should get back all the icloud stuff by logging in. not recommended if you want to keep everything.