This is a question I am throwing out to everyone. Let me give you the scenario below and I would like your suggestions (and reasoning) for items you recommend. Let's see what you come up with! SCENARIO: Extremely safely heat a small (12" x 20" ) thin wafer heating element with a small sized rechargeable battery source. Must be very safe, no overheating, no explosions, no overheating of battery pack, and as lightweight as possible. MUST be very economical and products already available in bulk production. -must reach heat setting extremely quickly (would like to hear sample time frames in your suggestions) -heating element encased on plastic mold, forming thin plastic sheet with small battery pack attached to it -"low" heat in the 90's F, "high" heat around 105+-F -Must reach desired heat setting and hold for 20 minutes+-, then will automatically shut off and not be used for many hours -Would prefer to get numerous uses from one charge, but at least 2-3 uses is required -battery pack needs to be in flat linear arrangement and can be the width of a single battery and as long as 15-20 inches(basically, can't stack the batteries, must align them in a straight line)...and remember, as light as possible -Does not have to cool quickly -battery pack will be inches away from the heating element -will also need to power battery life display, and low,high light -finished product will be form molded plastic encasing battery (with charging port exposed) and heating element with controls, etc. -finished product will be somewhat rigid, but will require slight flexing ability but will not be folded or creased, etc, like clothing Questions (***most ECONOMICAL avenue for all questions that would support mass production***): 1.) What is the smallest type and size battery pack that would provide numerous uses (20 minutes of usable heat with 3-12 hours of downtime) on a single charge? Question #2 may determine power source. 2.) What would be the most economical flat wafer heating element to use in this application (carbon fiber, Mica, aluminum sheet, etc.)? Question #1 may determine heating source. 3.)What would be the ultimate small rechargeable battery source paired with the ultimate wafer type heating element source that is currently on the market that could easily be paired together? Looking for point and click ideas that you would suggest if you had to pair these two items together today from readily available extremely economical products to mass produce this product. **Bonus**= On a lighter note, if money was no option and production/manufacturing was not a hindrance, what would you use!? NOTE: I am not a physicist but I think I've covered most of the variables that you should need to answer this question. If I've missed something major, please let me know. Thanks everyone!