These Lenz rcB 1400 Lithium Battery Packs put the power of warmth (for your toes) right at your fingertips. With three heating levels controllable via the Lenz app (or from the packs themselves), you can fine-tune your comfort for up to 14 hours. For those who prefer a more straightforward approach, you can also adjust between three heat settings directly on the pack perfect for when your phone’s busy playing your “Staying Toasty” playlist.