Winter care for the battery
I have a Trek FX bike. It's in an unheated garage. Temperatures here go below freezing in Winter about half the time. How should I care for the battery during the Winter. Right now it's at full charge (which is where I usually keep it). Any advice is appreciated.
Hopefully the three posts were a site glitch...
If the battery is removable, take it out and store it indoors, recharging it once a month. If not, charge it every month in the garage. If you can insulate it with something like fiberglass insulation, that may help.
The Trek FX bike, unless you've added something, is a non-electric bike. So if there is a battery, what kind is it? Or more specifically, what chemistry is the battery?
If it is a lithium pack, store it at about a 2/3 state of charge. Check the voltage about once a month to be sure it isn't self-discharging. You don't need to do anything else.
In the case of lead acid - keep fully charged and occasionally charge to be sure it stays fully charged. Most lead acid chargers have a "float" (aka "standby") mode, in which case it is best to keep the charger connected to the battery pack during storage - but only if the float voltage is correct (in some chargers, it is not). Check the voltage periodically. The volts per cell when on float should be per the "standby use table" here:
In either case, assuming you don't live in the Arctic region, the best place for storage of the battery pack IS in the unheated garage. This is particularly true for Lithiums. Typical sub-frezing temperatures won't hurt them and will improve their storage life. A fully charged lead acid battery will not freeze until -69C (-92F), although as a battery discharges, this freezing temperature goes up.
I think its a Lithium battery.
Naturally, you mean a type of Lithium-ion battery, a rechargeable battery. But you, under other circumstances, should be careful with the terminology. A lithium battery (without the -ion suffix) refers to a non-rechargeable battery, a so-called primary battery, like those used in some cameras.
Anyway, the capacity of a Li-ion battery deteriorates with time, regardless of use. And shelf life is reduced somewhat by high temperatures, not low.
"When not in use, store the battery in a cool place. For long-term storage, manufacturers recommend a 40 percent charge. This allows for some self-discharge while still retaining sufficient charge to keep the protection circuit active. Finding the ideal state-of-charge is not easy; this would require a discharge unit with an appropriate cut-off. Users should not worry too much about the state-of-charge; a cool and dry place is more important."
As a practical matter, you don't need to do much. Storing the bike in the cold garage is fine, and the battery's state of charge (SoC) during this period will have negligible effect on its capacity or cycle life. But keeping it in a SoC less than full is somewhat preferable.
However, winter doesn't mean death to e-biking. As long as the streets aren't slippery, don't be a pussy.
I had assumed it was an SLA battery. L* batteries do indeed store best between 1/2 and say, 7/8 charge.
Looks like we have a new troll here. 'Nehmo' seems to have something gratuitously nasty to say to just about everyone. This isn't usenet, Nehmo.
The only advice I've seen in this thread that I don't completely agree with is that it may be OK to store a fully charged LiMnO (the kind BionX uses) in freezing cold when fully charged. This wasn't stated exactly, but I believe it could be read that way.
The max charge capacity of a LiMnO cell goes down with the temperature, so fully charging one, then letting its temperature drop considerably may result in an overcharged, and damaged cell. The charge does not drop a lot, so storing a 3/4 charged cell in freezing temps should be fine.
My recommendation for storing a BionX battery over the winter is to fully charge it and store it inside. Wouldn't hurt to recharge it every month or two, either, but the recharge is not critical, as the charge should drop very little over many months.
"The max charge capacity of a LiMnO cell goes down with the temperature, so fully charging one, then letting its temperature drop considerably may result in an overcharged, and damaged cell."
It doesn't work that way. By "overcharging" we mean driving the charging voltage so high the active electrode materials are damaged. Cooling a battery cannot cause the voltage to go up, so cannot cause it to be overcharged. The loss of capacity if a li-ion cell with low temperature is due to increased internal resistance, so the voltage drop becomes excessive for a usable discharge rate at a low state of charge. The active materials still hold or release the same quantity of Li+ ions at low temperatures, but get too sluggish doing it.
The benefits of storing Li cells partially discharged is of a separate cause than temperatures. Partial discharge puts the crystal lattice of the anode and cathode material in a less "stretched-out" condition (i.e either material is not aren't "packed-full" of Li-ions). By analogy it is like a rubber band stored in a stretched-out condition losing it elasticity.
The other thing that degrades Li-cells is simply time. In fact, for most users, the present limitation on rechargable li-ion cells seems to be calender-life than charge cycles. Either the cathode materials (or the graphite anode matl?) seem to degrade over time no matter the number of charge cycles. This degradation happens slower at low temperatures. So storage at cold temperatures is beneficial. This is well established. There is certainly a sufficiently low temperature that will damage the cell, for example if the electrolyte freezes - but this happens at some temperature below, probably well below -43C (-45F) (the freezing point of pure diethyl Carbonate before other things are dissolved in it to make the electrolyte), so assuming you don't live up near the Arctic Circle, this is not a concern.
Congratulations on owning the best. You got what you paid for, zero headaches and lots of fun.
By now, you have probably realized BionX makes a proprietary system, not really interchangeable, but very useful. Proprietary systems are the rule, not the exception, in the 21st century. If a system isn't proprietary, it hasn't really been figured out. BionX figured it out, in one package, which can be used on any bike. If the (2) mounting holes aren't drilled (yet), no worries. That's what drills are for.
In winter, charge the battery and store it inside. These batteries do best from 55-95 degrees. Winter is an issue. Batteries discharge/charge better if you keep them from getting cold soaked while just sitting. Summertime, they won't even try to charge if the cases are too hot, so you seek some shade and try again when it's cooler.
I never heard of the concept of "cold soaked". Temperature is temperature. if they are not being charged or discharged, it is best to store them in a cold place. If small enough, in the refrigerator.
You know, anything I would have to say about BionX may NOT be true or accepted by other E bikers as well. A good fit, without wires hanging out everywhere, SEEMS to be better, only because I THINK it's better. Our winters here vary, from 60F to -30F. Temperature is temperature. Sometimes I ride the BionX bike when it's 10F. I guess I could just leave the NiMH battery on there and run the extension cord out to it and charge it overnight when it's -5F outside. I don't know if that would be right or not. So, no worries.
I guess BionX figured out how to make something people could use differently, and still get approximately the same results. My results aren't perfect, either, so it's nothing more than an uneducated hunch which compels me to remove the battery.
As for "cold soaked", somebody said it once to me and I didn't challenge it. So, thanks for doing so. BTW, the guy who said it had just sold me a replacement battery for my lawn mower, which I inadvertently left out in the winter temps and DESTROYED. That was $110 ago, and he said "cold soaked". Since then, for the last 10 years, I take the battery out and store it in the winter, because I don't want to get SOAKED for another $110.
And, the NiMH BionX battery is on its 6th season. Doesn't make me right, but it sure SEEMS to save $500 here and there...