UKC

Does anyone have any knowledge / recommendations for small power banks (10-20mAh) that work in extreme cold?

In reply to Rob Grant:

Watch battery?

In reply to Rob Grant:

What voltage? 5V USB i presume? What is it to charge exactly?

In reply to Rob Grant:

Sorry original post should read 10,000-20,000mAh

In reply to Dark-Cloud:

When people use mAh as a measure of capacity the answer is almost always 5V USB.

In reply to ianstevens:

Erm OK, apart from when it isn't, anyway it was very valid question given that he stated 10-20mAh!

In reply to Rob Grant:

5V USB power banks are what I am interested in.

In reply to Rob Grant:

I used one made by Anker during a cold trip to Finnmark in February. I find they turn themselves off in deep cold so that charging stops unless you keep them in your pocket. For this reason I bought the smaller 10,000mAh units as they are closer to pocket-sized.

In reply to Rob Grant:

I'm not aware of any that are designed for cold conditions, I'd be surprised. 

In a way, there's no substitute for keeping the thing warm. This might involve sticking the thing up your jumper anytime you want to use it. 

Only some general advice, 

If you know your power needs, add a x4 multiplier before you compare it to product specs, (possibly more if you really are looking at extreme cold)

Avoid "slim" products, and avoid anything that's has a metal enclosure (these are less pleasant to warm it up using your body temp)

In reply to norrisdan71:

No idea about cold temps but the Nitecore NB10000 at 155g is lighter than Anker and has proved excellent in use. Recommended by US backpacking blogs.

In reply to ianstevens:

I wonder if manufactures refer to the capacity of the underlying internal battery (a 3.7v lithium cell maybe) in their mAhr figures and not the actual output (5v) for a USB power bank.

Which might go some way to explaining unexpectedly low performance sometimes. 

Watt hours of delivered capacity would be a more honest value!

In reply to Rob Grant:

A friend of mine has an led Lenser one, uses changeable lithium cells and is very well built. Uses the same cells as his headtorch which seems a useful feature. 

None of them will hit their rated values the cold. Manufacturers will always specify capacity in ideal conditions. In addition to the cells loosing a lot of their oomph in the cold, the battery management circuit will cut off charge and discharge early when subjected to extreme temps as cell voltage varies with temperature. Cold is less of an issue than heat if you are pulling charge but the device you are charging is subject to the same issues so will cut off early too, but will appear to be at 100%. 

Basically its a loose loose loose situation for battery banks in the cold. Bad things can happen when you bring a battery back to room temps if you let the cells fully charge or discharge at an extreme temperature.

Your cheap knock off ones from the far east might not have as well developed management circuits built in and may be more willing to fly closer to the safety margins to squeeze bigger capacity numbers etc. But you really do not want a 20AH battery going up in smoke.

Buy a good one and work on the assumption it will never hit its rated capacity in the cold. Going bigger than you think you need will always help. Or better yet keep the battery bank and your devices warm.

In reply to Rob Grant:

We use the anker 633 magnetic charge. The unit is slightly thicker than most but it does give us more than the 1.5 phone charges that most units give and it doesn't create the heat that some older models do on magnetic charge. Like many will say, body heat I've found is the only way to stop batteries getting killed by the cold so I often buy tops that allow me to store them at chest level.

In reply to richard_hopkins:

That would be my guess. Every one of these things I've cracked open has just been a bunch of 18650s with a circuit board, regardless of manufacturer.

Agreed - I have some Goal Zero ones which are marketed with Wh - much more useful (especially as they have alternate outputs to USB). However, mAh seems to have become the standard - and I guess it's easier to market 20,000 xh rather than 74 Wh. Extending this though - it would make sense that it's at 3.7V, as the max power bank is about 25000 mAh - equating to 93 Wh, and falling just within hand luggage limits.  

In reply to Rob Grant: for what it’s worth, I carry a Belkin and Anker 20k each, in the rucsac during daytime and in my sleeping bag at night and they both retain significant capacity for four or five charges each but.....if I leave them out of the sleeping bag by mistake then minus 15C temp drains them significantly over one night. Either are fine with that routine to keep them warm. Main issue for me is they are heavy! regards Andrew

In reply to Rob Grant:

Lithium ion battery chemistry is what it is (irrespective of manufacturer), and it's temperature sensitive. You can get battery technology which work well in the cold but it's much more expensive and heavy for a given capacity. The only way to keep Li-ion batteries working to spec is to keep them warm. Waste body heat is the simplest solution.

In reply to Rob Grant:

My noname power bank is good for re-charging my iPhone 4-5 times. When it’s cold I have both inside my sleeping bag. Been using it this way down to -40C. 

In reply to Rob Grant:

Any!  You should always warm them up prior to use.

I've used cheap amazon ones (20 Ah) for expeditions where it gets to almost -40 and they've worked fine.  But, as others have said, they must be warmed first.

My routine once I've made camp is to pop one in my big down jacket that I'm wearing and let it warm for an hour.  Then I charge my electrics in the same pocket.  All done by bed time.

I previously used the sleeping bag but it became a tangled mess.  Jacket is much easier (I also have special 5cm long USB cables to avoid spaghetti).

In reply to crayefish:

The 5cm cable is a great idea. I’m well aquatinted with sleeping bag cable spaghetti!

And thanks everyone, that is some useful info so far.