USB or Battery Powered Tent Heater?

Someone smarter than me can address the actual physics and thermodynamics here, but I believe that the energy density of batteries, especially small portable batteries, is simply woefully inadequate of an energy storage medium for heating. Liquid or solid fuels and combustion are the way to go. Invest in a tent with a stove jack and a wood burning stove if you want to be toasty and happy for the part of the night when you are awake, and put some bottles of hot water in your bag for sleeping.

Here’s a rough analysis of cooking in the backcountry with batteries and other electric sources:

https://backpackinglight.com/forums/topic/80795/

Short version: It takes many pounds of batteries and accessories to bring two cups of water to boil. You really don’t want to heat a tent that way.

I bought my wife a combo USB battery / hand warmer recommended by The Wirecutter:

http://thewirecutter.com/reviews/the-best-hand-warmer/

A couple of hand warmers might help for short periods.

— Rex

Both Rex and Philip are spot on.

Your 26800 mAH battery stores about 26.8 amp-hours at 12V potential. Assuming one could draw all 26.8 amp-hours, one would have about 1.16 MJ of energy available.

But that’s not very much energy. The specific energy of wood, for example, is about 15 MJ/kg. So, a 75 gram (3 oz) stick has about as much useful energy as your battery (as it pertains to heating–don’t run outside and try to plug a stick into your cellphone to charge it).

Another caveat is the limited power distribution over USB. I thought it was limited to ten-ish watts, but a quick Google informed me that 100W is possible. So, you could run a 100W heater, but remember, you’ve only got 26.8 amp hours available, at 12V. Ignoring the inefficiencies of the power electronics that would be required, you’d only be able to run your 100W heater for a little over 3 hours, assuming you took your battery from full charge to zero.

So, a 100W heater, for about 3 hours. 100W is pretty small for a space heater.

However, a minor tangent: I grew up in WI, and we always used electric blankets in the winter months (August through June). It seems like one could design a relatively lightweight, small electric blanket to go in your bag with you. This could draw USB levels of power, and produce a noticeable amount of heat, since the heat is produced within your down cocoon. (edit to add: Rex basically mentioned this above with his wife’s hand warmers).

That’s mostly a thought experiment; the practicality of doing so based on the premise that you have extra, “free” electrical energy available–you are already carrying the charger and battery. Otherwise, it would be undoubtedly more efficient (in terms of weight carried) to simply bring a bag with another ounce or two of down.

Also batteries lose capacity as the temperatures goes down. In those temps, who/what is going to keep the batteries warm???

It won’t heat the whole tent but a Nalgene bottle with some hot water in your armpit or next to your femoral artery will provide a ton of warmth.

As Mark notes, batteries will lose a lot of efficiency in those temperatures.  Also, even on a sunny day the sun won’t be in the sky and above the treetops for very long in late December, so getting a full charge could be a challenge.

Putting the equivalent weight into insulation, or even into chemical hand warmers might be a better bet.

Walt

The closest battery powered option I’m aware of is the Rumple Puffe on Kickstarter; this approach would focus on heating you instead of your shelter.  I’m sure I overlooked it but I can’t find the weight.  Looking at their other non-electric blankets of a similar size and taking the weight of the battery bank into consideration, I very much doubt that it’s under 4.5 lbs for a device that can in ideal situations run 10 hours on low and adds multiple points of failure to a sleep system.  For the same weight penalty, you could bring an expedition worthy sleeping bag (eg MB -20*f @ 60.5 ounces) and a down jacket that don’t rely on batteries.

Hawt nalgene …. Youll likely be melting snow anyways for watah

;)

“Does anyone here speak Puffay?”

“I speak some Puffay.”

“What does ‘Hawt nalgene …. Youll likely be melting snow anyways for watah ;)’ mean?

“Ah!  Eric is explaining that you will need to melt snow to make water anyways so you can use your Nalgene bottle to keep you warm.”

“Thanks Eric and Mr. Puffay translator!”

POOFAY !!!

Wrapping ur hawt nalgenr in yr poofay when in da pack means u gotta nice warm jackets at stops …. N it keeps da watah HAWT

Just make shure dere r no leaks n that the outside is dry n free of snow

;)

Ha ha!  Touche!

Poofay.  Poofay.  Poofay.

I’ve written it three times to burn it into my memory so I won’t screw it up again.

Rumple Puffe :

“Both the natural down and the synthetic fill versions are 54″x80” when laid flat and can easily cover even the tallest travelers. The down version weighs just 2.1 lbs and compresses into a stuff sack that measures 6×12″, while the synthetic version weighs 3.4 lbs and packs down to 8×16″.’

That is the blanket only, no battery or charger.

Estimated delivery : July 2017