# Charging battery outside ideal 15-20c range



## confusedcyclist (6 Mar 2020)

Bosch claim "The ideal charging temperature is 15 to 20 degrees Celsius. If the battery temperature is below 0 degrees Celsius, the intelligent battery management system from Bosch prevents charging – in order to protect the battery cells."

Does anyone know what the long term impact of charging at >5C - <15C might be? Is it simply charging efficiency or cell longevity at stake. Notice how they state the intelligent system prevents damage. Does this mean it's safe to charge above 0C?

This time of my year my garage tends to be 10C, I'd like to stop bringing my battery in to the heated house overnight as it's a pain unlocking it and putting it back the bike twice a day. Charging on the bike would be ideal.


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## Pale Rider (6 Mar 2020)

confusedcyclist said:


> Does this mean it's safe to charge above 0C?



I'm sure I've charged mine a few times at close to freezing point.

No immediate sign of damage.

Not sure what damage is supposed to be done, but I might bring it indoors if I thought the temperature was minus an awful lot.

No point in worrying if it's zero and above.

Absolutely no point in worrying in March when it's a few degrees and above.


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## Levo-Lon (7 Mar 2020)

I'm pretty sure it's all down to charge capacity.
A warm battery will charge better than a very cold one.

I've charged mine on the bike outside in 3-10 deg but I usually do it indoors.

When I had a Bosch system I biked to work in cold weather and just took the battery off when I got to work, it just lasted longer.


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## confusedcyclist (7 Mar 2020)

My garage is integral, but not heated, but because the boiler is located in there it retains some waste heat, hence the slightly higher than outdoor temps. I wouldn't class it as indoors as it's not insulated, with a leaky garage door I'm sure the temps could fall lower overnight when the boiler isn't called for heat for up to 8 hours. Battery always comes indoors when the bike is stored in a rack outdoors at work, purely for security.


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## raleighnut (7 Mar 2020)

confusedcyclist said:


> My garage is integral, but not heated, but because the boiler is located in there it retains some waste heat, hence the slightly higher than outdoor temps. I wouldn't class it as indoors as it's not insulated, with a leaky garage door I'm sure the temps could fall lower overnight when the boiler isn't called for heat for up to 8 hours. Battery always comes indoors when the bike is stored in a rack outdoors at work, purely for security.


charge it at work


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## CXRAndy (7 Mar 2020)

There must be something to charging at an optimal temperature. My Tesla will spend a while warming the battery pack before applying charge current if its cold. Similarly preconditioning before arriving at a 125kw supercharger raises the battery temp to accept that amount of current


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## confusedcyclist (9 Mar 2020)

raleighnut said:


> charge it at work


The thought has crossed my mind since I would be brining it in anyway, and it's OK as a one off, but I'd be swapping the logistics of moving a battery around to moving a charger around instead, albeit the faff of locking is omitted. Leaving my charger at work isn't an option as the ride home depletes roughly 30% of my battery, any long evening riding outside commuting would become problematic. Bosch's chargers are silly expensive. I've set up an ebay search for second hand chargers, but these are not the kinds of things people sell frequently, so I'm not holding my breath for a bargain.


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## sheddy (9 Mar 2020)

I think we had this same question last month.


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## Pale Rider (9 Mar 2020)

Tempting to think Bosch, er, over charges for their chargers when others are available for thirty quid.

However, the electrical engineering of the Bosch system is the best on the market.

I'm not sure how much part the charger plays in that.

There seems to be a relay in mine because I can hear it clicking.

That might be because my bike has the dual battery system which the charger charges alternately a little at a time.


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## confusedcyclist (9 Mar 2020)

sheddy said:


> I think we had this same question last month.


Can you link to it, I didn't spot it?


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## confusedcyclist (9 Mar 2020)

Pale Rider said:


> There seems to be a relay in mine because I can hear it clicking.
> That might be because my bike has the dual battery system which the charger charges alternately a little at a time.



Yes, mine clicks as the charging starts, but as mine only charges a single battery, it's only heard once when it kicks in, maybe again when it reaches 100%, but I've never been present for the switch off at full charge.

It makes sense that it alternates the charge, if it charged one to full before the other, if you make a habit of interrupting the charging and then riding off, it will put more stress on the battery that gets more full charging/depletion cycles than the other. Alternating the charge and depletion keeps things as level as possible.

It's definitely a complex bit of kit as the electronics spends a bit of time thinking about the voltage before it's applied to the cells before charging starts. I've used an energy meter and it doesn't go all guns blazing when the switch is flipped.


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## Pale Rider (9 Mar 2020)

I don't claim to fully understand it, but it seems to work well.

Owners of generic Chinese chargers and batteries speak of sparks when connecting and disconnecting.

Eventually, this burns away the battery or cradle terminals.

Bosch may be dear, but you don't get nonsense like that.


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## confusedcyclist (9 Mar 2020)

I ran a completed listing search on ebay, and it looks like a few standard charges sold around Jan roughly £20-30 plus delivery a pop, I could justify that expense for the sake of convenience. Clearly though the second hand market is not very big, at least for now, in-garage charging is a sensible option.


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## raleighnut (9 Mar 2020)

Pale Rider said:


> I don't claim to fully understand it, but it seems to work well.
> 
> Owners of generic Chinese chargers and batteries speak of sparks when connecting and disconnecting.
> 
> ...


Mine says in the destructions to connect before turning the power on, maybe that is to avoid the sparking


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## Pale Rider (9 Mar 2020)

raleighnut said:


> Mine says in the destructions to connect before turning the power on, maybe that is to avoid the sparking



That's what I do, although I've read other opinion which says to power up the charger before plugging it into the battery.

Makes more sense to me to connect to the battery first, then connect the mains to the charger.


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## sheddy (9 Mar 2020)

Sorry last year
https://www.cyclechat.net/threads/temperature-and-battery.254524/#post-5776614


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## confusedcyclist (9 Mar 2020)

Thanks, there doesn't seem to be any discussion about the how's and why's for the stated ideal charging temperature ranges. As I say, if it's about charging rate, efficiency or achieving the highest possible charged state then I'm not so fussed, I just don't want to unecessarily shorten the useful lifespan, yet lugging a 625 watt battery around gets old fast! That said I'm happy to do it if there is a good reason. I'm already cycling between 20 and 80 % and using a smart timer to bring the battery up to 80% just before I depart for work to ensure the longest service life possible in a bid to reduce cost, both the financial and environmental impact that these batteries can have.

I might write to Bosch to find out.


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## Milkfloat (9 Mar 2020)

I charge my Bosch 36V whenever they have been used, I don't worry about levels or temperatures I just throw them on charge. I think all my batteries are at least 5 years old.


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## confusedcyclist (9 Mar 2020)

I've automated the process with a TP Link Kasa smart plug. Since my riding tends to be reliably the same day in day out, with only very minor variation, I've found I can set my charger on a schedule. Upon returning home the battery gets plugged in, the battery then has about 2 hours to return to room temperature up after a cold winter ride. Then the smart plug turns itself on after two hours for an hour and half only, to bring it up to about 60% of capacity. It then switches off again until 4am the next day when it finishes charging up to 80%, just before I depart at 6am. Weekends are also built into the schedule, charged to 60% when I return home, then off until Sunday night. Through a bit of trial and error, I'm within a few percentage points of these targets most of the time. With very little in the way of manual effort I should eek out some decent extra life from the battery. If for any reason I need 100% charge, I can set my charger on remotely with a smartphone or google assistant voice command. It's a pity the charger doesn't have this functionality built in, we're paying enough Bosch! I have thought about building my own app to calculate the charging times, but I've found there are too many variables I don't understand yet.

The two things you can do to maximise life are to cycle the battery between 20-80%, and store at around 60%. My system achieves both with nearly no effort. It was all invested up front by taking a few notes on when and how long the charge took to go up up in increments of 10%. If I had time to kill, I could probably work it out with more granular data in 5, 2 or even 1% increments, but what I've got works well enough for now.


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