Help with creating a low voltage heating element.

Hello

I have a project that I need help with.

I would like to create a heating element using low voltage, such as batteries, to make a heating element to 100 degrees Fahrenheit. I need it to last approximately 1-2 hours.

The smaller in size it is, the better . I need it to keep liquid at a 98 degrees Fahrenheit(+/- 3 degrees).

The liquid will be 7oz.

Any suggestions would be helpful.

Thanks

Look at December 15, How to make a low voltage heating element...about 3 pages into the past on this forum.