I have two hot water bottles but I rarely use them. They are still sold and used generally but not as much as they used to be. Homes are better insulated and heated now so there is less need. People also have other things - electric blankets, the item Lori described.

Yes it is called a hot water bottle. They were very common. I still have one. We can still buy them but instead many people buy cotton bags filled with grain that you heat in the microwave and put on your sore body. Easier to use.

I've seen it during my stay in China. I guess you can call it a "hot water bag/bottle. It's suitable for China but not here.

En Chile lo llamamos guatero y si, es muy popular 👍