The thing I find most people ask me about this hand warmer when they see me using it, is: “How warm or hot can that thing possibly get?!” I can’t speak for other hand warmers, but I feel like I hit the jackpot when randomly choosing this one - it’s exactly what I wanted. This KARECEL model is fantastic and can be both warm and hot, depending on what setting you set it to. The results exceeded my expectations. Here’s what I found: 1) You should know before you read the following points, that the unit operates in ranges (Low: 95F-107F, Medium: 104F-118F, High: 107F-130F). What that means is that the hand warmer does not operate at constant temperature. So when you’re using it at a particular setting, the unit’s temperature will tend to rise and fall within the posted ranges. While that may sound like a drawback, and maybe it is (sometimes it’s slightly frustrating), in reality it might actually be more of a bonus than it sounds. I can think of two reasons why the warmer might do that: A) It could be trying to ease the load on the battery so that the unit runs longer B) I think it may have been designed this way with human feel in mind - the body tends to become desensitized to anything that is constant. By varying the temperature in cycles, the device will still stay warm throughout, but as the hot range of the mode arrives, you can feel and appreciate it because your body is experiencing an increase in temperature. At constant temperature, once you’ve plateaued in terms of reaching a particular temperature, the hand warmer wouldn’t feel like it’s on anymore (see my comment below about using the hand warmer on low after you’ve been using it on a setting higher than that, and maybe that will help you to understand what I mean). 2) I didn’t expect something that is basically a portable battery powered electric heater to last more than 15-20 minutes with a battery capacity of 5200mAh. On the low setting, which I find to be good for when you’re indoors, it lasted around an hour on my initial try. To be fair, the battery may not have been fully charged when I unpacked it. I was also briefly playing around with the medium and high settings during that trial (though it was mostly on low), so the actual run time is probably more than an hour and could potentially be much much longer if kept on low. If I ever have a need to run it continuously for longer than an hour and the results are much longer, I might update this review to reflect that. 3) The medium setting, is the perfect temperature for when my hands are very cold. I found it to be the best balance between hot heat and battery life, and is good for use outside, and when you’re first coming inside from a cold chill. I also found that occasionally, it can get too hot to keep held barehanded once your hands have already heated up. In my opinion, that’s a good thing! The fact that this small battery powered device can do that at all, is quite amazing to me. Using the hand warmer at this temperature setting for a few minutes, then lowering the warmer back down to low, made it feel in my hands like the hand warmer wasn’t even turned on anymore. 4) The High setting can get HOT! Not hot enough to burn you, but hot enough that without something between your fingers and the warmer, it might feel like it could burn you, but won’t. Again, in my opinion, that’s a great thing! I find that the high setting would be best used when you’re outside in intense cold weather. This setting gives the warmer the most power and best chance to be strong enough to heat up against the cold. Keep in mind that the low end of this range is a very comfortable 107 degrees Fahrenheit, but it can climb up to 130 degrees which might be very uncomfortable for those with sensitive skin. You can always lower the warmer back down to a lower setting once you’ve reached the point where it feels like you’re holding fire in your hands. [UPDATE: After some quick research, apparently human skin can receive a 1st degree burn at 118 degrees Fahrenheit and 2nd degree burn at 131 degrees - so, BE CAREFUL!] 5) You can help kickstart the warmer to be its hottest at any setting (Low, Medium, High) by using it inside its pouch or inside a pocket. From there, you can take it out and use it at its best potency. The pouch also helps you hold the warmer (which has metal heating surfaces) a little bit more comfortably, during those times when it’s operating toward the high end of its range. 6) I didn’t purchase this product to be a charger for my cell phone. If you know about battery capacities, then you know this unit’s capacity should be enough to charge most smartphones from 0-100 about 2-3 times over — keep in mind, that is so long as you’re not actively using your cell phone and/or the warming function simultaneously while charging up your phone or miscellaneous USB device. Once you factor in doing either of those things, the ability to calculate how much or often this unit can charge your phone back up to 100%, is beyond my pay grade. That said, it’s got plenty of capacity and the USB port according to the manual is 2.0 Amps which means most devices will charge up fast when plugged into it. 7) In my experience, this hand warmer fully recharged up from 0-100% capacity in just a little bit over an hour. I thought that was incredible! To be fair, your mileage may vary depending on how powerful a charger you’re using - I recommend something that has at least a 2.0A output. 8) A quick double press of the power button will allow you to see how much battery life is available to you (Low, Medium, High). This is a very convenient feature considering that you’re left to just guessing if it wasn’t included. If the unit is currently warming, it shows what heat level you’re using with amber LED lights. The battery remaining feature displays using blue LED lights. If you’re using a heat setting and want to check the remaining battery life, the amber and blue LEDs mix to display in purple. It can be hard to figure out which LEDs are lit, and which ones are just receiving light from a nearby LED, so I would like to see this problem addressed in a redesign. 9) The hand warmer only needs about 30-60 seconds to get warm. I would suggest that it probably takes about 3-5 minutes to get hot. The amount of time it takes for you to perceive warmth will vary based on your current body temperature and the ambient temperature around you. The colder the hand warmer electronics are, the longer it seems to me that the unit takes to generate its heat. 10) KARECEL’S CUSTOMER SERVICE IS FANTASTIC! I cannot say enough good things about how much they care (or should I say, “kare”) about their customers. My unit arrived with a small scratch on it that bothered me a little bit, but didn’t affect its useability. The thing that really bothered me a lot was that after only using the unit 2-3 times, the wrist strap broke. I personally found that using a wrist strap with the warmer was highly convenient during those times when you wanted to give your hands a quick heat break, but still keep the unit close by ready to be grabbed again. It also acts as a safety tether just in case you accidentally drop the hand warmer. Anyways, I contacted KARECEL and they responded quickly within an hour and offered me a free replacement without any hassle. In addition to that, they offered me different options in terms of color, and also different methods for receiving it that may vary in the amount of time it would take to get to me. At the end of the day, I was provided with several options that put me in control of the customer experience - KARECEL just wanted to know how they could make me happy. I swear I never say this, but I would give a 6th star here if I could. Now how long this warmer will last me before breaking down, or the battery possibly doesn’t hold a charge, is something I just can’t tell you right now. But for the time being, with just a few uses in, I’m very satisfied with my investment in Winter comfort.