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Hotronic e4 Foot Warmer

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  • m4 comes with all you need to customize your ski, snowboard or hiking boots using insoles of your choice
  • Kit includes two battery packs with heat regulators, one pair of heating elements with coverings, and a recharger with American and European adapters
  • High-capacity, rechargeable batteries are designed for cold-temperature operation; battery packs attach outside for easy operation
  • Features four temperature/durations settings
  • Setting level one heats from 83° to 89° F (28° to 32° C) for 19 to 21 hours
  • Level two heats from 96° to 106° F (36° to 41° C) for seven to nine hours
  • Level three heats from 105° to 116° F (40° to 47° C) for five to 6.5 hours
  • Level four: 135° to 144° F (57° to 62° C) for 2.5 to 3.75 hours
  • Level four, which can be used in three-minute intervals or continously, is meant for a burst of heat; CAUTION: Using longer may result in burns
  • Battery pack LEDs indicate whether power is on or off and selected heating level; lights blink when heating level four is selected to run continuously
  • Advanced charging technology prevents overcharging

Insoles are not included in the kit; use those that come with the boots or select from insoles sold separately. Temperature ranges and durations are based on battery packs at minus 4° F (minus 20° C).


Item 745511

REI Membership

Hotronic e4 Foot Warmer Specs
Best use
(Single battery pack) 3 x 2.5 x 1 inches

Hotronic e4 Foot Warmer

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Rated 4.3636/5 based on 11 reviews
Rated 1out of5
by fromDo not buy I bought Hotronic boot heaters in 2004. The first problem was the battery cables broke, and the salesman at Christy Sports in Breckenridge blamed it on me, and charged for repair. The primary problem with them, however, is that they simply don't work as promised. They do not generate enough heat to do any good. My feet and toes still get numb from the cold. Please do NOT WASTE YOUR MONEY like I did.
Date published: 2012-02-20
Rated 2out of5
by fromtoo fragile I have used boot heaters for many years and have found the Hotronics to be poorly constructed. The boot heater cable is very fragile and severs easily. I use them in AT boots in the back country and at ski areas, and with the moving hinge of the boot, the cable slides into the boot and bunches up, therefore causing a bundle of cable in the boot. If I am not careful about loading the chairlift the cable can be pinched and then the boot heater no longer works. The heater itself has pulled apart and was returned to the manufacturer to be repaired and it no longer holds a charge as well as the other boot heater. I would not recommend the Hotronic boot heater if you are in ski boots the majority of the winter.
Date published: 2011-12-22
Rated 5out of5
by fromHappy Wife Bought these as a gift for my wife for Christmas this year. Was a little hesitant at first because of the price and lack of reviews online. Main reason for this purchase was a 6 day trip planned to Grand Targhee where it is notoriously cold. These were the ticket! With temps dipping well below zero on several days, we were able to stay out a lot longer than we would have without these. We opted just to mount them on her superfeet insoles, so if she wanted to wear them in different shoes she could. Easily adjustable and simple to use. We mounted them on the outside of my wife's boots and never had a problem with them coming loose. We charged them per the directions and have yet to have a problem. Can't wait to by the 100+cm extensions so she can wear them fly fishing this spring.
Date published: 2013-03-24
Rated 5out of5
by fromToasty Toes These have been a fantastic investment. I had REI install these into my ski boots and have skied with them a few times now. They keep my feet warm in even very chilly conditions. If you have Raynauld's or just get really cold feet when skiing, these are a must have winter item.
Date published: 2012-12-27
Rated 5out of5
by fromMust have Got these for myself last year, and for my family this xmas. Takes the stress of worrying about keeping your feet warm and not frostbitten out of the day. Makes all winter activities much more enjoyable. I carry them with me all the time in the backcountry or when I don't expect to be able to get indoors easily. Great to have an insurance policy against frostbite.
Date published: 2013-01-02
Rated 5out of5
by fromWorth the price We got these to try to resolve the problem my wife had with cold feet while skiing. Had tried adhesive foot warmers and a boot toe cover that helped some, but still didn't solve her problem. Happy to say these work great. Although expensive, they're worth it when nothing else works. The only issues we had were originally having the units mounted on the inside leg side of the boot on the boot strap because that appeared to be about the only place they would fit. It's easy to hit them together there, and my wife did loose one, although fortunately someone had picked it up and we were able to recover it. Since then she's moved to the front shin area on the boot tongue pullup loop, and has secured the clip with a velcro band she made. That seems to have resolved the problem.
Date published: 2013-02-06
Rated 5out of5
by fromWorth the Money I work outside in all winter weather conditions. I have always had problems with cold feet in the winter as the day goes on. Previously I relied on a combination of socks and single use disposable air activated heaters. The air actived heaters are good on an occasional basis, but the price adds up for everyday use and heat output cannot be adjusted. The Hotronic system allows me to move the heated insoles to the boots I will need for the day. I was a bit hesitant to try it due to the price, but since REI has always backed the products they sell I decided to give these a try. I have been a member since 1971. The Hotronic system allows four temperature settings which can be adjusted as needed. Turn them up whe outside and turn them down or off when inside for awhile. Heavier well insulated boots require minimum heat while ordinary boots require more. With other insoles and various length cords, the batteries can be attached directly to some boots or attached to the belt. The on and off buttons require a steady push and hold which reduces the chance of turning them up or off by momentary contact. The fact the batteries can be recharged overnight will eventually pay for itself over the single use disposable heaters. The only drawback I see is the lack of a power level gauge to warn you the batteries are low. For extended use at the top two heat levels, another set of batteries may be needed. While these seem to have been intended for use with ski boots, they work well with a variety of boots.
Date published: 2013-11-25
Rated 5out of5
by from"Cure" for Raynaud's The negatives: For how much they charge for this product I would have expected the quality insole Hotronic makes to be supplied with this kit. The box leads you to believe you are getting a new insole, when in fact you are getting a fuzzy sticker to hold the unit in place on your old insole. The GOOD: They flat out work. Previously, anything below 60 degrees and my feet are frozen. I wear insulated boots and have been playing with different combinations of layers and thicknesses of socks without success. Heating my boots in the morning only lasted an hour at the most. I plugged these in, cranked them up and sat in a cold room for 6 hours during a lecture without cold feet. It's been 3 years since this has happened to me! The unit is barely noticeable in the sole, but you will need to play with placement of the wires, battery pack and heating pad to achieve this. Definitely worth the investment, especially for people with Raynaud's or other circulatory issues.
Date published: 2013-12-06

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