How I explain post-exertional malaise to people who don't get it

I use this analogy now: imagine you have a phone with a battery that only charges to 30%. If you use 30%, the phone works. If you use 31%, the phone doesn't just run slow — it breaks, and takes three days to repair itself. People seem to understand that in a way 'fatigue' never conveyed. The key is the time delay — the crash doesn't happen during the activity, it happens 12-48 hours later. That's the part that's impossible to explain without an analogy.