Keep your battery warm

[flecc]

We did discuss it Scott, and have often advised keeping a battery indoors overnight to give a warm morning start.

The problem with trying to insulate it is the way they fit between frame and mudguard and the closeness of chains etc, it's difficult to devise anything that completely seals out icy blasts of air. I always store my batteries indoors but find they lose temperature very rapidly when taken out into single figure temperatures, slowing the performance. As you say, that's regardless of type, all chemical reactions slow with dropping temperature, and they're usually best at 30 to 60 degrees C. Sadly we don't often get into that band in the UK.
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[prState]

Ah, here's something I've been meaning to ask. I don't ride up a lot of steep grades but I've been wondering how the batteries (Like li-on on ezees) do with a starting outdoor temp around 45 degrees C? That's generally the worst of the summer here. (sometimes it gets even hotter but usually not too many days a year, and it's so miserable at that point I usually don't go out anyway)

I never noticed a problem with my Nimh with high temps here. I assume the battery gets warmer as it used as well? Would those kind of temps shorten the life?

 

[flecc]

No problem on the operation as I've indicated, the efficiency would be high.

There would be no measurable effect on the life as it's fairly constant throughout the range of normal operating temperatures and beyond to around 60 degrees C.

Apart from the lowered performance when cold, the only time temperature becomes relevant is when a li-ion is to be stored out of use, when it's best at close to zero degrees C with between 20% and 40% charge. Then only 2% of life is lost each year, but the battery must not be frozen.
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[giguana]

perhaps a lunchbox with some kind of thermostat heater like a vivarium heater.

 

[rsscott]

Or you can get those 'rechargeable' heat-pads and stick them to the battery casing!

I have some reusable ones which you boil in water once you have used them.

 

[faphillips]

The G-Wiz electric car has electrically powered battery heaters to improve performance. Not sure if they are powered by the very batteries they are trying to keep warm or mains powered. Could one easily make an electric blanket for a cycle battery and is it likely to be worthwhile. I guess it would need to be thermostatically controlled - although judging by the number of days we actually get into the 30c to 60c range perhaps it would be be better left on permanently.

 

[flecc]

The most effective way would be to have the insulated heater wire inside the battery case, but I think the current drain would cancel any performance benefit.
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[Sector]

Maplins heated clothing

1) I've been told by a man who knows these things that the companies that supply portable radio equipment to the police force and elsewhere are looking at fitting heaters to warm the LiIon batteries in cold conditions.

2) Maplins are selling off heated gloves and jackets at the moment. Each item has AA batteries to provide the heat. Could possibly be a good starting point for DIY battery heater experimentation? I wonder if they have any protection against overheating or if they rely on the wearer to have the sense to switch off.

3) My contact also says that real life experience with the (relativley small capacity) LiIon batteries in portable radio transceivers confirms working life of 400 to 500 recharges.

 

[flecc]

3) My contact also says that real life experience with the (relativley small capacity) LiIon batteries in portable radio transceivers confirms working life of 400 to 500 recharges.

The longest lives are in satellites where perfectly ordinary Li-ions run to over 3600 charges. That's because each daily discharge is only one seventh of capacity, followed by the one seventh charge, and the loadings are both constant and low.

In the worst cases on our bikes, the most powerful motors make them suffer very high loadings, they sometimes get run down to empty, and the charge discharge conditions are irregular.
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[Ian]

Another battery life reducing factor in e-bikes is the fact that even a moderate loss of capacity will render the battery useless for many users purposes. A mobile phone or laptop battery, and possibly a police transceiver battery will still be perfectly usable at 30% of its original capacity but few people would consider a bike battery usable after a similar loss.

Most of my real life experience of Li-ions is with laptop computers which I use daily at work, charge/discharge patterns vary but are probably equivalent to 3 or 4 cycles a week, compete discharging probably happens on average once a week, some charges are partial while others are complete and often combined with several hours running on mains power.

My current work laptop is a Dell, just coming up to one year old and the battery that ran it for 4 hours when new is now down to about two and a half hours, still perfectly usable for a computer, but if it was powering a bike I would be concerned about the substantial loss of range. My previous computer was an IBM and suffered a similar rapid loss of capacity, as did its predecessor, a Compaq. My personal laptop is an Apple and had a battery life of about 3 years in spite of only being used very rarely on battery power, The end of life point being zero remaining capacity, far beyond what would usable on a bike.