The battery probably made it slow: https://arstechnica.com/tech-policy/2020/11/apple-settles-wi...

> I replaced my iPhone 6 because it was slow, not because battery was bad

iPhone slowness can go hand in hand with batteries going bad, especially in the iPhone 6 days. Apple phones will limit peak performance when it detects the battery voltage can't handle it without too much of a voltage drop. From what I understand its now an opt-out setting, but for most of the iPhone 6's life it wasn't an option.

If you opt out of it your phone will suddenly turn off, which is definitely not an improvement over being slow. Having the opt-out is nonsense and an example of bad regulation.

This isn't the only reason an old phone would be slow though, batteries are not the only consumable component in a phone.

For sure. I've had devices slow down from storage wearing out as well.

The software slows the phone down so not create current spikes that the aged battery cant handle

Do you remember the whole phone throttling issue on a bad battery?