We tested how much heat five of the most popular rechargeable hand warmers produced, and how long their batteries lasted.

They’re affordable. If you buy the warmers in bulk, they cost about 75¢ per pair. (A full box is about $30 for 40 pairs.) The HotHands Hand Warmers come two to a pack. Michael Hession/NYT ...

Temperatures of each hand warmer (in Fahrenheit) from the first minute of activation until their temp dropped below 100 degrees. I ran a separate test of the best electric hand warmers and the best ...

If you're over those squishy, shake-activated hand warmers and want something a little more high-tech for those chilly ...

At an all-time low price of $23, these multitasking gizmos offer hours of heat — plus they can keep your phone juiced up.

The first 'reaction' that we tried for our hand warmer involved dissolving potassium carbonate (K 2 CO 3) in water. Potassium carbonate is one of the chemicals left behind in the ashes of burnt wood.