As a gift, I received a Mophie Juice Pack Helium (1500 mAh).

After reading the manual and affirming it was at full charge, I tested it. AFAIK, it worked as designed (sorta). Charging my iPhone occurred as expected. But what was a surprise, is how hot the Mophie got.

About 45 minutes in to the test, I noticed that the Mophie was very warm. (Lacking a thermalcouple or such, I term it as “uncomfortably warm”.) Ergo, I promptly quit the charging and shut down my phone. Even after removing the Mophie, the back of my phone was warm, very warm.

I checked for discoloration & bulging, but there was none. And all seems normal with no ill effects. But should there be latent battery or iOS issues, I no knot.

I called Mophie Tech Support and they advised that heat is a common by-product & residual effect of the charging process, but would gladly exchange my device (at no cost) for a new one. And so they did.

The new Mophie works the same, but as I was far more attentive, I did not allow it get as hot as before.

I would use the Mophie in an emergency, but until I can better monitor the temperature, I remain gun shy and the Mophie awaits regifting.

Wadda think? Is this thermal thingy typical of all juice packs? Am I being prudent or paranoid?

Right below this thread is one concerning chargers, where the topic of hot chargers and safety came up. I'd suggest reading my post that covers the topic pretty thoroughly

Paranoia is often prudent.

See V1's excellent post in the following thread.

It was, in fact, V1, your thread that prompted me to post as I did. Not withstanding data indicating "not to worry", I'll try be to prudently paranoid and keep my tool cool (a term I've not used in a great many years).

BTW, your tutorial was very helpful. Many thanks!

thx. If you still have a question or concern that I didn't address, let me know. I thought you were still looking for an answer to something.