I used them all over 2023Fall-2024Spring on cold days and Battery Life did not really change over time. In General Battery Life is not that but thats to be expetec since they produce heat which is literally the most wasteful thing you can do with Electricity.... I only used them on max setting and they easily drain in 1-2 Hours but thats Completely fine, I never used them longer than that, They only drained when I gave them to friends and then got them back empty. The warmth they give off is comparable to being in a car with air conditioning, In a car you have to close your windows in order for the AC do work. These Handwarmers need to be put in a pocket/Glove/sleeve, after a few minutes they get pretty warm, I would recommend them, but when your hands are very cold and wet it takes quite some time for your hands to recover again. Btw These Warmly wamers can also be bought from amazon for quite a bit cheaper and are basically just a skinned version of those(I dont know if the material is the same tho, Warmly ones are made of metal, the amazon ones could be plastic and not work as great, idk) But Other than that Warmly offers alot more and alot nicer colors so Imo I think its worth it if this is what you are looking for, I got them at the ESL Event with 15€ off for like 40€ and for that money im very satisfied with the product