Portable bottle warmer

Mamas I want a portable bottle warmer. Something that is easy to use and convenient on the go.

With my first born it was hard to breastfeeding in some places. Some malls don't have any nursing rooms and when I try to use the changing rooms almost all of them had curtains which made it hard for me. I'm not comfortable when I know someone is near or outside. I cave a nursing cover on but I cant get comfortable. So I'm planning this time if I'm out the house to have a pumped milk with me (in a cold bag) so that why I need bottle warmer something easy and fast to use.

Please recommend some products that might help.