Anyone tried battery heated gear like gloves, hoodies or socks?

My younger brother works outdoors for the city parks department, and he's a tough SOB but I always feel bad for him on miserable, cold rainy days. Looking to get him some sort of heating clothing to try out at work for Christmas. Any of you guys who work or play outside in the cold a lot have any experience? Are they worth it or just a sham?

I was looking at some heated socks or insoles on Amazon. They say on medium/low the battery should last all day but I dono how well any of this amazon shit is made and don't trust their reviews anymore... I especially don't want to burn the kid or blow his toes off