Lifespan of Lithium Polymer batteries?

[Synthman]

I would like to know how much capacity these batteries would lose per year if they are left unused. I know temperature has something to do with it as I've heard on numerous occasions that they last longer if placed in a freezer! I use cordless professional power tools quite often and some of them run on Li-ion. Also heard they last longer if stored with a 50% charge. But really all I want to know is how much it would decrease in storage from the point of manufacture without being used?

 

[HarryB]

How to prolong lithium-based batteries I am not sure we are a big enough group to add to this. Most of us don't store our batteries as we are too busy out riding most days. If I did I would pop it in the fridge (not freezer) and leave it at 50% charge. If it is a decent battery it won't lose much in a year.

PS Unless it is a panasonic battery you will need to take it out and give it a top up charge every couple of months or so. The BMS will gradually drain the battery and you don't want it to end up at 0 charge as that really would kill the battery.

 

[NRG]

Freezing will kill the battery, stored at 40~50% charge and below 10c they should last a long time. I think Flecc keeps his laptop battery in the fridge and it's lasted years.

 

[flecc]

I think Flecc keeps his laptop battery in the fridge and it's lasted years.

Yes, it's there now at about 5 degrees C and will be 6 years old next year.

Cold storage is only worth it for long terms though, I only travel with my laptop a couple of times a year for example. After each battery use I charge to about 20 to 40% and it goes back onto the floor of the fridge wrapped in clingfilm.

If using an e-bike at least once a month it's not worth it, the stress of contantly bringing the cells up to temperature and full charging will probably reduce the life as much as any saving made.

Most current e-bike lithium batteries are good for about two years life with usable range, a bit less sometimes if used daily for high mileages or a bit longer if intermittently used for lower mileages. They do chemically deteriorate with age though, so very light use doesn't mean very long life with full capacity.

It's not possible to define accurately how much capacity is lost per annum since the constant developments are improving this. It was originally about 35% of the year's starting capacity per annum lost, but that's probably down to under 20% with the best ones now.

All the above is for lithium batteries with manganese or compound cathodes. The not commonly used newest type with iron based cathodes (LiFePO4, known as Lithium Iron Phosphate) can last around two or three times as long, depending on the application.
.

 

[tangent]

At the moment I charge my battery every day even though I only really need to charge every other day. This does give me better performance because the first half of the battery provides a higher load EMF than the second half. From what I have read, it would not make much difference to battery longevity if I charged every other day instead. Is this the case?

The battery is a LiMn Panasonic 26V 10Ah, as used on Kalkhoff's.

 

[flecc]

If you use anywhere near half the charge each day tangent, stick to daily charging.

Basically lithium batteries are like car lead acid batteries in this respect, they like charging little and often, not deep discharging and fully charging which shortens the life of the cells.

That's one of the things that makes them perfect for e-bikes since, as you've noted, it means optimum performance every day.
.

 

[Synthman]

Yeah I thought freezing them sounded a bit odd. My Battery is a Phylion, and it states to charge "2 hours per 2 months" but my bike is used pretty much every day, I have done 110 charges and I reckon its done about 1000 miles in 8 months. My first thread mentions my battery was already more than a couple of years old when I got the bike, which is why I wanted to know how much (percentage) it had lost in that time. I now estimate that to be 30-40% at room temperature, but I will never know. As for the refrigeration method, I was considering it for some of my power tool batteries and maybe for a laptop battery in the future!

 

[joab]

My Li-MN battery (EZEE) is now 3 years old (manufacturing date) and has 413 cycles. Still has 6ah out of 9,6ah.
Regards,
Jo

 

[Synthman]

How do you measure the amps? I've got two multimeters, they both measure the volts ok, one is 12 years old and can only measure DC current of 200ma, and my other one came with a tool kit and can do 10ADC on the unfused test lead socket. I tried it a few times, and this time I blew the tip of the probe off. In fact there's always a spark when I try to measure the amps but not the volts. Reckon my battery is over 10ah and I need a meter that can measure 20ADC?

 

[jbond]

How do you measure the amps? I've got two multimeters, they both measure the volts ok, one is 12 years old and can only measure DC current of 200ma, and my other one came with a tool kit and can do 10ADC on the unfused test lead socket. I tried it a few times, and this time I blew the tip of the probe off. In fact there's always a spark when I try to measure the amps but not the volts. Reckon my battery is over 10ah and I need a meter that can measure 20ADC?

You need a The Cycle Analyst Homepage - Ebike Amp-Hour and Watt Meter cost ya, though.

 

[daniel.weck]

You need a The Cycle Analyst Homepage - Ebike Amp-Hour and Watt Meter cost ya, though.

Yep, that's a 100 GBP product. You can get a much cheaper 30 GBP power meter though.

http://www.pedelecs.co.uk/forum/electric-bicycles/4821-watts-up-vs-turnigy-power-meter-analyser.html#post60953

 

[tangent]

How do you measure the amps? I've got two multimeters, they both measure the volts ok, one is 12 years old and can only measure DC current of 200ma, and my other one came with a tool kit and can do 10ADC on the unfused test lead socket. I tried it a few times, and this time I blew the tip of the probe off. In fact there's always a spark when I try to measure the amps but not the volts. Reckon my battery is over 10ah and I need a meter that can measure 20ADC?

I would not advise you to try that again! You are shorting out the battery and cannot measure Ah that way. You are lucky it was the tip of the probe that got blown off. This could have done irreparable damage to the battery, or to you.

To measure the Ah capacity you need to connect a power meter in series with your bike motor or a suitable load of around 3-4 ohms and then run until the voltage drops to around 3V per cell. For a 36V battery that would be about 30V. If testing off the bike, you need something that can take the power output of around 400W. e.g. power resistors connected to a large heatsink, or 12V 50W halogen bulbs arranged as 3 in series by 2 parallel. If testing off the bike, be very careful to not short the battery and make sure the load can handle the power.

 

[joab]

Yes I use the CA, another benefit of the CA is that it allows me to limit the amps I get from the battery. Sure that is streching the battery life. My amps today are on 8a giving me +- 280w.
Regards,
Jo

 

[Synthman]

I thought it would be the case that it needed a load. My expereince is limited to model railways and basic household electric. I would rather do this measurement on the bike but there will be an issue of how to connect the multimeter up, and will I be able to see it while riding. Those cheaper power meters look like the sort of thing I'm after, but I'm not too confident about wiring it up myself.