Winter battery care - how to look after battery when not in use for a few months

[pn_day]

Hi all,

I've been enjoying commuting to work a couple of times a week on the ebike - the combination of a 36V 20Ah battery in the frame and beefy CST rear hub mean that hills and headwinds are no longer such a problem

The icy weather appears to be on us, and roads are getting a bit slippery. There is therefore a distinct possibility that I might not be the bike for a couple of months.(I have bought studded tires, but SWMBO has had some strong words to say about cycling on ice!)

I've read a few comments from folks on here that batteries should be partially charged, not fully charged if they are to be left on the shelf for a while.

The cheap charger I have from BMS battery just seems to be based on voltage - it charges until the 36V battery reads 42V then stops.

Does anyone have an idea on how to partially charge suitable for storage, what level to charge to, and how often to top it up? Is this feasible with the cheap BMS battery chargers, or should I get a more sophisticated battery for this type of thing?

Thanks,
Phil

 

[Geebee]

I don't know what others do but I just fully charge the battery after each ride, over winter I put them on the charger every couple of months if not used, nearly always with the result of instant green light.
My oldest battery is heading into its 4th year (3rd in use) with zero deterioration noticeable, I have Hobby King LiPo's kept the same way and showing no signs of age and I think 2 years old.
Make of that what you will

 

[pn_day]

Thanks Geebee. Good to know that if I could get away with it if I just charge fully.
I'm envious of your recumbent trikes by the way. Do you use them all year round?

 

[JohnCade]

I think the usual advice from the dealers is to keep it at about two thirds to three quarters charged to prevent the - probably - slight risk of cell damage from being left a long time fully charged. Keep it indoors at room temperature and charge it up a bit every month or so. You can just ride it until it's down to about two thirds and then store it.

 

[Geebee]

Health issues limit my riding to better weather now, but yes I used to ride 6 days/nights a week all year round including sub zero evenings as long as it wasn't raining

 

[pn_day]

Thanks John. Useful feedback.

 

[flecc]

The state of charge can make less difference to battery ageing in storage than temperature, it's the temperature that is important. Have a look at the link below and scroll down a short way to the temperatures chart. There you'll see how for lithium how little the loss of capacity differs when at zero degrees C, but how much larger the loss is at 25 degrees C or more.

In other words, keep the battery in as cool a place as possible, but not below freezing as that can damage it. Also have it at a lower charge if possible to save a bit more capacity. Since such storage is mostly done in Winter, in the UK we don't have too much difficulty finding somewhere cold.

But also read the text at the start of the webpage, warning against charging when very cold. When bringing the battery back into use, bring it up to a higher temperature like room temperature over a few hours first.

Link to Battery University
.

 

[Geebee]

Flecc, that would make sense in my case as the bikes/trikes are kept in the house in less used rooms so cooler than the main rooms especially through winter when the bikes are used less.
I was aware that the lower storage voltage was better but my research matches your comments, ie. its a minor difference in longevity so I dont bother with it.

Ah well, good night all my bed is calling

 

[JohnCade]

The state of charge can make less difference to battery ageing in storage than temperature, it's the temperature that is important. Have a look at the link below and scroll down a short way to the temperatures chart. There you'll see how for lithium how little the loss of capacity differs when at zero degrees C, but how much larger the loss is at 25 degrees C or more.

In other words, keep the battery in as cool a place as possible, but not below freezing as that can damage it. Also have it at a lower charge if possible to save a bit more capacity. Since such storage is mostly done in Winter, in the UK we don't have too much difficulty finding somewhere cold.

But also read the text at the start of the webpage, warning against charging when very cold. When bringing the battery back into use, bring it up to a higher temperature like room temperature over a few hours first.

Link to Battery University
.

That's different flecc. Most of the dealers tell you to store at room temperature and not leave the battery anywhere where the temperature drops below 15 degrees. Matt Goodes at 50 Cycles even told me that the battery should not be left in an unheated garage in early autumn in case the nighttime temperature drops below 15 degrees.

 

[flecc]

I can assure you they are very wrong John, who would you rather trust, a dealer or the industry expert who runs the Battery University site. Make sure they mean Centigrade though, if they are using Fahrenheit the 15 degree lower limit will be too low!

Matt's advice, if he's referring to Centigrade, goes against all other advice on this subject, and it's frankly a bit ridiculous. Not only are temperatures below 15 degrees C a normal temperature much of the year in the UK, but there are many owners of e-bikes with satisfactory battery life in places like Norway and Sweden where it never gets up to 15 degrees C in Winter! That includes the members from that location who have posted pictures of themselves well wrapped up and with their e-bike in deep snow .
.

 

[pn_day]

Thanks Flecc for the link and the helpful commentary (particularly about warming up before charging).

Fortunately it's all worked out well. My ebike is relegated to a small box room which also happens to not have the heating up very high, so sounds like if I charge to something over 40% and leave it in the cool room it should be fine.

Thanks chaps. Once again the knowledge on this forum has helped me to not make some expensive mistakes.

 

[JohnCade]

I think they meant above 15 degrees for storage not use.

I expect he's right, but it does go against what all the dealers sites say. So much conflicting info....

This for instance:

https://www.e-bikeshop.co.uk/blog/post/how-to-look-after-and-extend-the-life-of-your-bosch-ebike-battery/

I took this para from it.

The Bosch batteries are capable of being stored in temperatures between -10 through to +60 degrees centigrade. But the cells don’t like to be stored in very low or very high temperatures. In fact the best possible temperature for storage is room temperature. Around 15-20 degrees is perfect. So the eBike can stay in the shed but bring the battery inside with you.

 

[flecc]

That explains much John, it's probably where these dealers are getting this from, given the huge range of e-bikes using the Bosch unit. But there's very sources that agree with them.

Thats fine if one isn't interested in maximising battery life in storage, but storing at near to zero degrees C maximises the life. I've posted in here a number of times how my old laptop's battery is still good for most of it's original duration and it's now well over ten years old, I think twelve. That's quite exceptional, but it's entirely due to it being most of it's life at near zero low down at the back of my fridge. I only need battery power a couple of times a year when away but if I'd stored at room temperature it would have been dead long ago from natural capacity decay rather than usage.

Of course Bosch won't be upset by users having to buy a new battery occasionally!

For the majority who don't store for very long periods, as Geebee says above, special methods aren't worth bothering with, best to just use and enjoy, which is probably what Bosch are saying.
.

 

[JamesW]

ahhh, but if you were a dealer/manufacturer, you would want to sell more batteries wouldn't you! so you might give advice that positively encouraged battery degredation even if you knew different, especially if all you competitors are doing it! Increase the turnover.

Doesn't surprise me the different advice coming from different areas!

 

[JohnCade]

For the majority who don't store for very long periods, as Geebee says above, special methods aren't worth bothering with, best to just use and enjoy, which is probably what Bosch are saying.
.

No I'm not planning to store the battery over winter, and it shuts down and goes to sleep after a week anyway.

But apropo of 50 Cycles comment. That came after I'd contacted them about a fault with it, and they did replace it under warranty. So right or wrong it might be the best policy to follow the dealer's advice in case a problem does develop with a battery...

If for instance someone did store a battery for a few months at a low temperature, and for whatever reason it developed a fault. It probably wouldn't be much use telling the dealer you ignored what they said and took advice from the web - however informed or even right the website was.

 

[JamesW]

the only time I haven't followed their advice is when I couldn't!

 

[flecc]

If for instance someone did store a battery for a few months at a low temperature, and for whatever reason it developed a fault. It probably wouldn't be much use telling the dealer you ignored what they said and took advice from the web - however informed or even right the website was.

True, but clearly the 15 degrees advice is nonsense, whether Centigrade or Fahrenheit, storage or use. I'm quite sure Bosch wouldn't support it, given that 15 degrees C and less is normal in Germany for much of the year.

One doesn't need to be a battery expert to know the truth, simply because batteries are chemical devices, not electrical. As such, chemical reactions are slowed at lower temperatures, extending the life of the reactants.
.

 

[JohnCade]

It was Centigrade. I don't think many people use Fahrenheit any more. I was a bit surprised when he said that. It crossed my mind that he might be looking for excuses on the warranty front at first. But I am an old cynic...

I was planning to start bringing the battery into the house when it got colder, but I didn't think 15 degrees was cold. Still I followed his advice with the new battery and now it's colder anyway.

 

[JamesW]

It was Centigrade. I don't think many people use Fahrenheit any more. I was a bit surprised when he said that. It crossed my mind that he might be looking for excuses on the warranty front at first. But I am an old cynic...

I was planning to start bringing the battery into the house when it got colder, but I didn't think 15 degrees was cold. Still I followed his advice with the new battery and now it's colder anyway.

most Americans use degF still!

 

[JohnCade]

most Americans use degF still!

Yes I know but I'm not an American. How are you liking it here in the old country BTW?