symptoms of a defective battery

Randylea wrote:

Will a defective battery get hot and result in a slow processor

I’m unsure if this is a theoretical question, or if there is an actual bad battery here.

Yes, a bad battery can produce heat.

But a busy processor, active display backlighting, active memory, and active storage can each also all get hot.

And heat can cause a processor to throttle performance, yes.

If you do have a defective battery, that can potentially cause other issues, including swelling. Which can be quite destructive to an iPhone.