Just posting a brief* follow-up on this:
PowerGlider External Battery Case for HTC One (M7)
Still providing promised charging rate of approx 80%.
Today was the 1st time I actually ran the phone down to less than 5% before turning the case on.I left the phone powered on & for the most part & let it sit idle just to see how much the case would charge the phone.Charging stopped @ 75%,so,I'd say that's right about on target,taking away a bit for energy loss from power xfer from the case & power consumed during stand-by.
Your results will be even better when having both the phone & case charged to 100%,then run the case power down 1st,eliminating most of the power loss due to re-charging from case-to-phone.
Prior results I experienced w/the MOPHIE case & the GALAXY S3 were virtually identical,so,unless you happen to favor the MOPHIE brand,I'd go w/the I-BLASON model & save yourself $40.
*So much for brevity...........................