Battery vs Cold
 

Sadly, eBikes tend to suffer from the cold.
Beyond the universal thickening of lubrication, stiff bearings etc.
Cold seems to decrease both, the output rate of the battery and the batteries capacity.
http://cdn.twospoke.com/forum/attach...our-legs-_.jpg
This malady seems to be fairly universal.
Best known are lead acid batteries on frosty mornings ... the grumbling of the motor trying to turn over, followed by the dreaded """click click click!"
SLA are noticeably affected, as are Nimh, Ni-cd, Li-ion, LiFePO4 and ... ?
Even alkalines ... flashlights seem dimmer when cold.
Output is reduced due to the cold increasing electrical resistance of certain components.
Increased IR (Internal Resistance).

Of course, cold does thicken all lubrication, causing pedals, crank, chain, freewheel, hub, motor ... everything ... to require more power to operate.

I've noticed,specifically with Li-ion cells, that the cold hinders the free flow of electrons.
Heavy throttle use demonstrates as a deeper sag in pack voltage, which provides restricted performance and prematurely indicates a low battery condition-warning.

While it might be difficult-inconvenient to warm and keep warm your entire bicycle, most battery packs are removable and can be stored in warm location till used. Additionally, it is recommended to add insulation around cells. A base of polystyrene foam and surrounding with closed cell foam, fiberglass, any insulation, helps.
Ideal are soft sided coolers, lunch bags etc.
They come in a great variety of sizes and qualities.
I took a 6 pack cooler and added a base of non-compressible polystyrene, topped with a 7/16" layer of waferboard ... for rigidity and protection.

I store my pack inside, next to a heater vent, keeps it nice and warm 80ish F.
While batteries should not be charged while overly-warmish, they do, discharge, perform much better at warmer temperature - not HOT! - 80 towards 100F.

I did consider the option of a pack heater.
After considering need and functionability ... I decided that I, personally, did not want to spend extended lengths of time in the cold, so prolonged battery exposure would be unlikely or seldom.

For those interested, I did find and research small, sheet type, heating elements.
While 12V rated, they could be run from 24-36V+ by running in series.
I will try to find my research and post it up.

Everyone knows that cold degrades your batteries performance.

Solutions?

Insulate your pack.
For Li-ion, LiPo, LiFePO4 etc, insulated lunch bags, 6pack coolers etc, provide nice thermal protection.
Pre-warm your pack.
or ... add heat packs, gelled preferred, liquid might not be recommended!

Found a nifty little item that might be the best-cheapest solution!

Inexpensive, thin, flexible, self adhesive, low wattage heating pads.

Perfect for eBike battery packs!
Will run preliminary tests with separate power source, 3S Li-ion. To measure drain & performance increase.

Ordered a few pairs, from China ...
Thought about it some more, ordered a few more pairs!
But might take a couple weeks ... will post review, as soon as possible.

Use your better judgment with batteries that tend to heat up, SLA, NiMh, RC Lipo etc.

As you mention battery packs can be removed to keep warm indoors when not in use and insulated sufficiently for internal heat generated during use to keep them warm enough while on the go.

The battery issue isn't what has significantly limited my ability to use electric power during winter months but rather problems with the actual motors. Shattered plastic components in geared hubs and mid-drives where the plastic gets brittle in the cold. Contraction expansion problems with the internal mechanics of motors, I've had seized bearings where one part warmed up and expanded while the other was still cold. I've also had moisture condensate and then freeze and break magnets loose from the outer ring glue bonding on out-runner type motors. And of course there is always the electrical and wear problems that come from the bike being constantly coated with half frozen road slosh goo crud.

Until they actually build the actual drive unit to be both completely sealed weather tight and with components that won't become brittle in the cold or have contraction/expansion binding issues that bind things up or break bonded magnets and other components loose there are going to be issues beyond just the battery. I've come close combining certain components that are better then others like those that have actual metal gears and cast aluminum housings for the outer motor casing and sealing the controller and electrical componets inside weather proof casings with lots of silicon calking and such but have yet to come up with an actual drive system that will meet my level of reliability and "Winter Proof" status beyond battery issues alone. I'm getting closer but haven't yet cracked it using available components.

But then again my standards for "Reliably Winter Proof" are probably higher then most. Most other people probably don't expect 100% reliability with only normal slight maintenance all winter in any and all weather conditions from sloppy freezing mud and slush goop mix coating the entire bike and the drive components nearly an inch thick in some areas to climbing a mountain pass at -40 below zero. My expectations are 100% winter proof reliability with only normal maintenance in any and all weather conditions including when most sane people don't want to travel by car on the roads much less an e-bike.

Just pointing out it isn't just the battery and there are other parts of the system where winter weather failures need to be addressed as well. So far some of the better sealed direct drive hub-motors with custom modifications namely, custom bearing change out (ceramics), Grease pack fiber disk shaft seals, and internal oil coating to prevent moisture impregnation used as a mid-drive in stoker-monkey type set-up with carefully sealed electrical components is the best combination I've found.

Wow, interesting. I haven't thought about the motor components having such a hard time in below freezing weather.

It's entirely possible to build electrical motors that can operate in extreme cold temperatures, same goes for gear boxes (usually reducing planetary gears for bike electric motors). Same goes for electronics and electrical components that is sealed against the weather.

It just requires a level of engineering and quality control that as far as I've seen most electric motors built for bicycles lack.

And, no, I don't think its just a "china junk" issue. I doubt even the most expensive U.S. and high end European engineered drives had the engineering team build the unit to work with critical task reliability level when its well below zero and its constantly getting coated with a freezing nasty goo consisting of half melted snow, road salt, and road debris and dirt from the spray of passing cars and go through multiple thaw freeze cycles as the motor repeatably goes from stone cold to warm and back again with every stop along the way where the rider leaves the bike outside the store long enough for the motor to cool back down to outside winter temperature and then heat back up (unevenly) when its put back to work for the trip to the next shopping location.

For e-bikes to fulfill a serious transportation roll in our society they need to have true all weather functionality from the heat of the desert in mid-day to a gale force storm with torrential rains and salt surf blowing in on the wind on a coastal road to the hard brutal treatment of deep cold and road salt half frozen crud mix of hard winter daily riding. The readily available stock, off the shelf, e-bike drive technology isn't quite up to that level as of yet.

I'm not putting the technology down, rather I'm pointing out an area where improvements need to be made.