# Trying to run a portable can heater on a different battery, I have a few questions

Hi! My brother has a small micro-heater that runs on a single AA battery. The battery life tends to be rather short so we started using rechargeable batteries. The rechargeable batteries are marked as 2000mAh and since they're AA and Nickel-metal Hydride I'm guessing they operate at 1.25v.

I want to mod it for use with a rechargeable cell phone battery. But I have a few questions about that.

1. The cell phone battery is marked as 3.7v, 930mAh, 3.4Wh and is a Li-ion battery. Is it safe to use a Li-ion battery? The NiMH batteries tend to heat up, will this damage the cell phone battery?

2. Assuming P=IV and V=IR hold true here, would I just have to add a resistor to decrease the current and send the same power to the heater? Is it really that easy?

3. Would there be any difference in sending a higher voltage and lower current to the heater if it receives the same power?

4. Given the cell phone battery is running with a higher resistance, would it last longer than two AA batteries? If its not, then this project isn't worth it.

88 views and no replies? Does anyone have any speculation on the answers?

uart

88 views and no replies? Does anyone have any speculation on the answers?
What type of heater is it. I mean, what does it heat.

The short answer is no, it's probably is not a good idea to try and run that from anything too different from it's rated voltage, certainly not a phone battery. Post more details about the nature of the heater, especially it's voltage and current and/or power ratings.

sophiecentaur
Gold Member

Lithium batteries are brilliant but only when run as they are designed to. Steer clear unless you know what any particular battery is rated at and can present it with the right load.
BTW, you can't operate a simple heater with 'higher volts and lower current' because its resistance is what it is. More volts will give you more current (I=V/R)
Primary cells are actually pretty high capacity so they tend to last well - they just cost a bit to replace.

Your cell phone battery only has 3.4Wh. A 2000mAh AA NiMH battery has about 2.4 Wh. So why not use 2 NiMH batteries?
What do you want to use that heater for? You could also use a hand warmer.
http://en.wikipedia.org/wiki/Hand_warmer
A sodium acetate hand warmer weights usually 200g and releases 14 Wh of heat. More than 5 times the energy of a AA battery. A hand warmer powered by lighter fluid gives you even a lot more energy. Just a drop of lighter fluid releases more heat than a battery. (10Wh per ml)

sophiecentaur