As a chronic pain sufferer, I have some expertise that I thought that I should share (because I am a narcissist) about heating pads. Which is this: the more handy accoutrements a heating pad has is directly proportionate to how poorly it heats up.
It's true. When I was wee, I broke both of my knees (yes, cry for me Argentina!) and so began a lifelong battle with aches when it rains. [I've been like the old lady prognosticator, predicting rain since I was a mere kidlet.] Add to that the various bumps and breaks and general aches of life, throw in a revolting reproductive system and viola! The perfect storm of an achy lady. So, you can trust me when I share with you my wisdom of the heating pad.
I have tried every brand/size/variety and along the way killed them all. Yes, I have actually used them until the on/off switch no longer functions. That's pretty sad, now that I think about it. And I have been on a quest to find a heating pad with just a 2 nice qualities: it has to get really hot and it should have an auto-off function. So far, bupkis.
Currently, I use a model that's made for lower back aches. It has an extra wide heating surface and "arms" on it that reach around your abdomen and velcro together so that it stays in place. I love it because I can attach it to my back or hips or even wind it around my knees and go to sleep! Because it also turns itself off! However, it doesn't get very hot. My last heating pad was awesome because it would scald you -- literally, if you laid on it, you'd get red welts! -- but that was also because it wouldn't turn itself off. So if you went to sleep with a backache, you woke up at some point in the night with a burning pain and tender flesh. While I appreciated the extra heat, it was often more hassle than it was worth. I did, however, use it until one day it just... died. The control couldn't take one more cycle. It probably burned through its own wires or something (although it was probably 10 years old).
Sadly, it seems that the want for heat and auto turn off are incompatible. Unless I want to invest in a self-timer switch for the outlet, like the one we use for the Christmas tree. But that seems too bothersome, especially when you're sweating through the pain of a back spasm -- the last thing you want to do is fiddle with a timer.
So heed my warning, weary travelers with aches and pains. Take your anti-inflammatories early and often!