Search for ski boot heated insoles. They pretty much all have external batteries though, as the nature of an insole means the power supply just can't be built in to it.
Thank you from a very cold house
@Leshaches started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
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Search for ski boot heated insoles. They pretty much all have external batteries though, as the nature of an insole means the power supply just can't be built in to it.