Cold Weather Storage and Charging Questions Answered

[doates625]

TLDR: I reached out to Stark Future with cold weather questions and suggested a built-in battery heater for cold weather charging and storage. The rep answered my questions, loved the suggestion, and passed it onto the engineers.

I asked the questions below:

"I have an unheated garage and where I live it gets down to under 10F (-12C). If I leave the bike plugged into the charger and set to 50% with the new software:

1. Will it warm the battery enough to let it charge (> 0C), or does the battery only have a cooler?

If it only has a cooler, I suggest future models have a battery heater for cold climates that runs off the charger when plugged in and can be turned on and off via the Stark Varg phone app.

2. Will it keep the battery topped off at 50% and counteract phantom drain, or will the battery drain indefinitely after reaching 50% the first time and require I unplug and plug it in again?

3. If it does top off, how much does the battery drain (in %) before it starts topping off again?"

I just got back a great detailed response with some interesting insights I thought would be worth sharing:

"Thank you for your detailed questions regarding the battery management in cold climates. Here are the answers to your queries:

1. Battery Heating: The current models typically have a cooling system but may not have a dedicated battery heater. If the battery is exposed to temperatures below 0°C (32°F), it may not charge effectively. Your suggestion for a battery heater that operates when plugged in is excellent and could be beneficial for future models. I will pass this feedback along to the development team.
2. Topping Off the Battery: If you leave the bike plugged in at 50%, it should maintain that level and counteract phantom drain. However, the specifics can depend on the battery management system. In some cases, it may require unplugging and plugging back in if the battery drains significantly.
3. Battery Drain Before Topping Off: The exact percentage at which the battery will start topping off again can vary based on the battery management system's settings. Typically, it may start to recharge when it drops to around 40-45%, but this can differ.

Please let us know if there’s anything else we can assist you with."

In short, if you leave the Stark Varg plugged in and set to 50% charge, it should maintain at 40-50%, with the should being a CYA. Still wise to check every few weeks to be sure. I'm replying to ask if battery charging is throttled or disabled automatically by SW at cold temperatures or if it's the responsibility of the user, and will try to remember to post the reply when I get it.

 

[doates625]

Q: Is the charging power requested by the user through the Stark Phone limited or disabled automatically by software when the battery detects cold temperatures, or is that the responsibility of the user?

A: The charging power management in cold temperatures is typically handled by the bike's software.
The system is designed to ensure safe charging conditions, which means that if the battery detects temperatures that are too low for safe charging, the software may automatically limit or disable charging to protect the battery. This is generally not something the user needs to manage manually.
However, it's always a good practice to monitor the charging process, especially in extreme temperatures, to ensure everything is functioning as expected.

 

[AL_V]

Interesting, it sounds like Stark is recommending leaving the charger on the bike indefinitely.
They used to recommend unplugging the charger and not leaving it connected.
This may have changed when they added the charge limiting sliders.

 

[doates625]

Yeah I think before you shouldn't have left it plugged in because storing at 100% degrades battery capacity (best to store at around 50%). But now that it can limit to 50% while plugged in it's easiest just to plug in. I left it plugged in at 50% at near minimum power around 200-300W for a week and came back and it was at 50%. Best charging habit for longevity is minimum power up to around 50%.

 

[Aleksandar13]

Yeah I think before you shouldn't have left it plugged in because storing at 100% degrades battery capacity (best to store at around 50%). But now that it can limit to 50% while plugged in it's easiest just to plug in. I left it plugged in at 50% at near minimum power around 200-300W for a week and came back and it was at 50%. Best charging habit for longevity is minimum power up to around 50%.

Thanks for posting this , I haven’t been aware of this and will plug this in today and leave as you’ve suggested !

 

[doates625]

I'm going to close off this thread by citing my sources:

Stark Varg Owner's Manual:
- "Chemical composition of the battery": "Lithium-ion"
- "To store the Stark VARG:" ...
- "Make sure the storage temperature is
between 0 and 30 ºC, with a preferred
storage temperature of 10 ºC." (10*C = 50*F)
- "Make sure that the battery charge
is between 30% and 50%."
- "Check the charge of the battery
regularly. If the charge drops below
30%, recharge the battery to 50%."
- "Do not charge a battery at temperatures below 4*C (40*F)"

Engineering Explained:

How To Ruin Your Electric Car's Battery - NMC Edition!

- Don't store at 100% charge for long periods, especially when it's hot
- Leave it plugged in: "A bunch of small charges is much better than infrequent full-depth charges"

Does Fast Charging Ruin Your Electric Car's Battery?

- "Studies have repeatedly shown that the faster your charging rate, the more degradation a battery has."
- Charging in cold temperatures also accelerates battery degradation
- Fast charging specifically at high SOC degrades the battery (I've personally seen the Stark Varg BMS slow down charging automatically as it approaches 100% - not a concern)
- Charging at 20C (68F) accelerates lithium plating (one form of battery degradation) far less than 15C, which is better than 10C, which is better than 5C. The minimum of 4C in the manual should be avoided if possible (*)

(*) Chicken Hawk Racing sells a Stark Varg battery warmer for $685 + shipping for those with a budget and an unheated storage unit in cold climates. You have to call their phone as it's not listed online. It heats the battery to 70F.

I suggest watching the videos to get the full nuance and details. Ultimately, charging to 50% (with a battery warmer if needed) at minimum power for storage, then charging to 100% at the minimum power time allows before a long ride is the best way to go.

 

[Aleksandar13]

One qs regarding charging when at home ! I guess if the bike stays in the garage for 1 week without riding or more it’s on constant slow charge with max at 50%, and when it reaches that level it will stop charging !
1.Do you then unplug and check the battery level and start charging again at 30%?
2. Before a ride , is it best to charge the bike a night before to 100% on slow charge and leave it plugged in or fast charge a few hours before the ride ?!

 

[Beagle]

These are all very reasonable considerations, and thanks for Stark answers.

One thing to keep in mind is the significance of each factor, their real world impact on battery performance and cycle life will vary from one battery cell to another.

Everything in there is true, but how much battery cells would be affected by charging at low temperature or by keeping cells at full charge will really depend on the battery type of course (NMC, NCA, LFP) and on battery cells themselves. For instance just between Molicel P42A, P45B and P50B the effect of such parameters could be quite different.

One last thing, "fast charge" for a Varg is basically plugging it to your standard household outlet (so far), that is very different from what is considered fast charge for a car.

Better safe than sorry, just we don't really how much it would impact the battery pack life, these general rules apply to all or most cells but the effect will vary.

 

[doates625]

One qs regarding charging when at home ! I guess if the bike stays in the garage for 1 week without riding or more it’s on constant slow charge with max at 50%, and when it reaches that level it will stop charging !
1.Do you then unplug and check the battery level and start charging again at 30%?
2. Before a ride , is it best to charge the bike a night before to 100% on slow charge and leave it plugged in or fast charge a few hours before the ride ?!

1. My test results and Stark's answers indicate you can leave it plugged in indefinitely now, so long as you set it to 50%. However, it's still wise to check it's state of charge regularly. I think they say every 2 weeks.

2. In the grand scheme of things, either is fine. As was stated in a previous reply, even "Fast charging" for the Stark Varg at 220V is only 1/2 C (charge rate) which is slow in the grand scheme of things. I personally would leave plugged in overnight at min power in case you forget to charge in the morning.

For example: (100% - 50%) * 6.48 kWh / 8h = 405W, so if you charge from 50% to 100% overnight (8 hours) at 400W it will be topped off right as you wake up.