As someone that likes to walk a lot but suffers from cold hands a lot, I was quite happy getting the chance to review a hand warmer. I have to admit, this niche of gadgets has been overlooked by me in the past, I just didn't know you could get them, so it is quite a unique thing to review.
Unlike hand warmers I have used in the past that fit in your glove and use chemicals to provide warmth, the Pisen is essentially a USB power bank that also uses its charge to work as a handwarmer. It uses a 7500mAh battery, which should be good enough to keep your phone going for a prolonged day out. It also has a sort of pebble shape which curves naturally around your grip. The overall design and build are quite impressive.
The first thing I noticed was that it is very large compared to old-fashioned hand warmers, so you are not going to slip this into your glove easily, apart from perhaps skiing mittens. It is also an individual unit, so you can only heat one hand at a time, which seems like a bit of a design flaw. Ideally, it would be good if this was half the size and was supplied as a pair, but then I am not sure how well it would work as a phone charger.
In practice, it is surprisingly good. I, fortunately, got my sample during the current cold snap, so temperatures in Blackpool are hovering around -1 throughout the day with a wind chill going up to -7. So, whenever I leave the house, I was wearing a large vintage peacoat with my hands remaining firmly placed in its pockets. The Pisen sits quite comfortable in a coat pocket, its overall size and shape don't provide any bulge in a heavy winter coat, and my hand curves around it nicely.
It takes a little while to heat up, but once it does, it lets off a significant amount of heat. There is a massive difference between using it outside of my coat pocket and inside, inside the heat would build up that it was bordering on too hot sometimes, whereas outside of my pocket it was just warm to touch. I didn't find this a bad thing, but some people may find it a bit too hot to touch occasionally. Only being able to warm one hand at a time is annoying at first but after 15 mins or so you can swap pockets and let the residual warmth keep one hand warm while the Pisen works on the other.
As a phone charger, it works well and does exactly what it is supposed to, and managed to top up my LG V20 on a long day out.
Priced at around £20 it is only marginally more expensive than other 7500mAh battery packs, so I think it is priced competitively with the added hand warmer function.