Keep battery warm in the winter

[esselius]

The thing with those discharge curves is that due to constant drain they heat up themselves.
Colder and older batteries more from elevated internal resistance.
High performance from hot batteries is why you see very small penalties in high drain graphs.
If you would let them cool let's say 10 times during one cycle it would be another graph (and
longer cycle life aswell).
From experience of Swedish winters I'd say it's no problem if you keep the bike indoor -so you start
off at room temperature and more importantly let the battery warm up an hour or so before start charging.
Also avoid regen on a <+5 degrees battery...

 

[markz]

What would happen if you left a fully charged battery out in the cold say -15C(+5F) overnight?
Then as stated ^^^^^^^^^^^ but you brought it in to warm up, or heated the battery pack up before riding.

 

[DrkAngel]

Charging and discharging when cold, hot too, is considered bad for Lithium cells!
However, storage, as low as 0ºC 32ºF, is considered advantageous.

 

[dogman dan]

Letting it freeze is not supposed to harm the battery. But you must get it above freezing before you charge it or ride it again.

Once really froze, it will not thaw quick. lots of thermal mass there. If its going to be a big problem, you need a thermometer sensor in the middle of that thing. So you know when it does finally thaw.

 

[TheBeastie]

I have to say I never really noticed the capacity degradation of winter vs summer in the past but I took my ebike for a 20km long run up the city (40km round trip) to a friends place that is about a 100meter higher elevation than where I live and I couldn't believe how much capacity I had once I got back home after the round trip total. And I realized the one difference was that it was a warm first summer day of 32c when most of the days have been average 15c and even cooler in the underground car park where I keep my ebike.

So it was the warmer weather that gave a nice kick of capacity/distance.

 

[DrkAngel]

.
... Thermostat control and low watt heating pads. < $3
Capable of self, or external, power.

 

[Learning Curve]

I am on Salt Spring Island, which is in between Victoria and Vancouver in Southern BC, and every winter I start worrying about whether my lithium battery is warm enough to charge without risking damage. I could bring the battery in, but it is a Juiced Cargo bike and it's a nuisance unscrewing 4 hard to reach bolts and then reattaching everything. I usually just do this when the weather stays below freezing for more than a couple hours. My house is up steep steps so bringing the bike in isn't an option, and it's in an unheated woodshed. I only go to town every couple weeks, so when it is colder than 7 Celsius I use a small 250 watt heater on the ground a foot away from the bike and throw a cover over the back of the bike and the heater. This warms up the air around the bike battery to 20 C pretty quick.

But once I start, I'm not sure how long it takes to warm the interior of the battery ? If it went down to 2 C overnight, and is now 4 C, how long would the battery need to be surrounded by 20 C air to warm up the insides of the battery to be safe to charge?

 

[99t4]

But once I start, I'm not sure how long it takes to warm the interior of the battery ? If it went down to 2 C overnight, and is now 4 C, how long would the battery need to be surrounded by 20 C air to warm up the insides of the battery to be safe to charge?

That is an interesting question. Depends on the shape of the battery, mainly how deep it is. As in thin strips of bacon cook faster than the center of a big thick ham.

How about putting the heater on an appropriately rated timer and set it to start 3-4 hours before charging? Slow cooker even heating theory.

If it's a thin stick shape type of battery maybe could get away with less preheat time.

 

[tomjasz]

My way...

 

[dogman dan]

Well, for starters 2c is not below freezing water. I'm not sure what temp lithium battery solvents freeze. When we talk about don't charge a frozen battery, we are talking about one taken from a deep freeze storage, or a place where its way below 0c all the time at night, or even in day.

But ideally, you'd plan ahead enough to put the bike to bed charged, then just warm the battery a few hours before you start to ride. No problem if the thing never froze solid. It may perform poorly, but its cold, not frozen.

At some point, you just have to live with some things that are not ideal for the lifespan of your battery. But the range it can operate in is actually quite wide.

 

[tomjasz]

Minnesota winter commuting needs a warming setup to have decent performance. A warmed battery quickly loses all warmth quickly.

 

[dogman dan]

Yes. I found while I was commuting, that starting out in 20F weather with a 70 degree battery left me enough performance. Range dropped, and voltage dropped.

But I quickly gave up trying to commute if it was any colder than 20F. It just cost me too much range if it was 15F, to make it all 15 miles to work. I did put some insulation around the battery too, some thin foam that helped. Sometimes I would go back to the half commute, leave the car ten miles from work. But mostly if it was that cold, I drove to work.

Loved riding to work though, when it was only 25-35 F. Arrived feeling quite refreshed and ready to work. Car ride, I'd start feeling lazy.

 

[markz]

Heating pads would be what I am looking into, use another battery to power it.
In the winter just ride where you have to go, and use a backpack for the battery, insulate the backpack and put in some reflective materials. My two batteries weigh a lot to do that, and it only nets me 50km (30 miles) for 1500wh in the summer, in the winter its much less.

All this winter talk makes me want to accelerate buying a vehicle but old used vehicles are just to expensive, the only way around the premium prices owners of the vehicles want is to go to auctions but its all online now, there is no rush of excitement on the auction block. or eating their greasy food. Surely you can go to the lot to check the vehicle out before purchasing, but test driving is not apart of that, only start it up so you dont get to see the vehicle drive from its parking spot, wait in line and hit the auction block. Maybe plug into the diagnostic port to see codes. If you cancel your insurance, it sky rockets thanks to private insurance vs government insurance (BC,SK)

 

[wineboyrider]

Yes. I found while I was commuting, that starting out in 20F weather with a 70 degree battery left me enough performance. Range dropped, and voltage dropped.

But I quickly gave up trying to commute if it was any colder than 20F. It just cost me too much range if it was 15F, to make it all 15 miles to work. I did put some insulation around the battery too, some thin foam that helped. Sometimes I would go back to the half commute, leave the car ten miles from work. But mostly if it was that cold, I drove to work.

Loved riding to work though, when it was only 25-35 F. Arrived feeling quite refreshed and ready to work. Car ride, I'd start feeling lazy.

Hand warmers at Walmart are pretty cheap now?

 

[Monte]

I live in Finland and wintertime temperatures can easily go below -20 C.

Last winter I did some checking with the battery pack temp before and after rides.

I keep my bike inside in a cellar, which sits at around 10 ... 15 C in the wintertime. Doing a 12 km commute starting with my pack at this 10 ... 15 C temp, the pack was at 23 ... 25 C after my ride to work.

So in this case I had no reason to cover the pack up with insulation, as it was already staying at a good temperature even when it was -25 C outside.

This of course totally depends on how hard the battery is pushed during use. In my case I average around 1 kW battery power on my commute, and my pack is approx 0,7 kWh in capacity, equalling about a 1,5C discharge rate. At this rate, the MJ1 cells easily produce enough heat to keep the pack itself warm. I'd guess the situation would be totally different at a 0,2C rate.

Although I wasn't losing capacity to the low temperature, the snow does greatly increase my wh/km consumption though, and where I would be going 45 km/h in the summer I was only going 28 ... 35 km/h depending on the amount on snow.

 

[ebike4healthandfitness]

I plan to get the BBS02 set with battery that goes on the frame to cycle to work in the winter and as we get temperatures as low as -15C here in Czech Republic I am worried about battery life getting drastically decreased, so I would like to keep it warm as much as possible.

There are some covers like https://www.e-bikeshop.co.uk/fahrer-bosch-battery-cover-ebike-2013-2014 however I think that might not be freeze proof enough, so I am thinking about some active solution.

Is there any thermophore(hot water bottle) system that would wrap around the battery or some electric mini pad heater that would use the USB port on the battery?

Or any other solution that you use, ideally DIY so it's also cost effective?

I am assuming the BBS02 is being used because of hills? If so, then maybe a better option is a GMAC hub or direct drive hub so you can use regen. With Regen (ideally variable Regen) you would have charging (in addition to discharge) to also keep your battery at a warm temp.