The belt takes around 4 hours to fully charge and can't be used while plugged in but once charged it lasts for around 2 hours on the higher heat settings. There are 4 levels of heat to choose from and while none of them are quite as hot as I expected I find the 3rd level very good for muscle aches or period pain.
The belt is made of a really soft material that is comfortable against the skin and because it held in place by velcro it is very easy to make it sit in a good position on your body. I have used it on my lower back, stomach and across the top of my shoulders and it easily stays in place whether you are sitting down or up and moving around.
It's handy that you can use the belt indoors or outside (as long as it's not raining) and the product is also machine washable which I think is a fantastic feature.
I do wish the temperature settings went slightly higher but overall I'd say this is a good product if you suffer with back pain or even if you want something to take the chill off (I live in a house with no central heating so often sit with this placed across the top of my shoulders in the evening and it's surprising how warm it keeps me!).