Bottle Warmer A-Level Idea

[DannyH10]

I am currently studying A level Engineering and am undertaking a feasibility study of the possibility of designing and making a marketable product that can warm liquids (such as milk for children or hot drinks) to a certain temperature and maintain it at that temperature. I have looked at existing products and noticed that most of these products require a mains supply or are USB powered. My suggestion is for the product to be truly portable and require no external power to operate - for use while Camping or at a festival etc.
I have several ideas of how to achieve this but have very little experience in this field.
Any thoughts relating to this topic would be greatly appreciated.

I used to have a bottle warmer that contained one of those automatic warmers that you click and it causes a chemical reaction.
Can’t remember exactly what they are Called but you often get them in hand warmers for walkers or similar.

Look at Rocket Fuel and Heat Genie

Thanks for your thoughts I will definitely look into these suggestions.
Do you believe there is a need for a product like this?

Why not go to some mother and baby groups and ask them?