What is inside the GM batteries?

[GM Brazil]

I found this topic on ES forum:

http://www.endless-sphere.com/forums/viewtopic.php?f=4&t=8452 (go to page 7 for the cheap battery)

He tested the e-bikekit.com battery and opened it to check the quality, and buy some from ebay sellers to compare with, see the difference:


Box BMS and battery pack from the Good e-bikekit.com battery:
http://www.ypedal.com/EBK/ES7.JPG
http://www.ypedal.com/EBK/ES10.JPG
http://www.ypedal.com/EBK/ES2.JPG
(examples from this page: http://www.ypedal.com/EBK/ebk.htm)

The cheap battery:
http://www.endless-sphere.com/forums/download/file.php?id=20707
http://www.endless-sphere.com/forums/download/file.php?id=20710
http://www.endless-sphere.com/forums/download/file.php?id=20712


Both are externally similar to GM batteries!

Witch type of quality the GM battery fits?

[PJames]

I had a 36v 16ah goldenmotor battery for couple months. I am happy with it. I've not opened it up and don't have the ability to test it beyond the voltage. What I can say is that compared to my old 36v 12ah sla batteries it is way lighter and has more capacity.  The comparision you give is not really a good verus bad, but really a good verus better. When people claim their more expensive hardware is better they are justiyfing the cost. The other batteries likely are better, but are they better enough to justify the price increase?

[GM Brazil]

I found it!

For sure it is a very better quality if compared to the paper rolls of the ES post. It is not LiFePO4 as I thought, but is as good as it, LiMn.

Pics of an open GM battery from this forum: http://elbilforum.no/forum/index.php?topic=2136.0

http://elbilforum.no/forum/index.php?action=dlattach;topic=2136.0;attach=1103;image
http://elbilforum.no/forum/index.php?action=dlattach;topic=2136.0;attach=1105;image
http://elbilforum.no/forum/index.php?action=dlattach;topic=2136.0;attach=1107;image

[ggielen]

Still it is at the very least confusing that the battery name is 'LFP' which would lead practically anyone with any form of a deductive capability to think it was in fact a LiFePo4. I'm not going to butkiss anyone at GM and just say that they should change the name, as this one is misleading.

On a more practical side, it is important that the end user is well aware of what type of battery he/she is getting/has got:
- how many charge cycles lifetime?
- power decay over time?
- best charging practice? (I've read no deep cycle charging for LiFePo4 in the first 20 cycles as a recommended practice to 'break in' the battery, how about LiMa?)
- memory properties?

And one question I have:
What is considered a charging cycle? Fully depleted battery to fully refilled = 1 cycle, that seems self-evident, but what about 50% empty battery recharged to 100%, is that 1 cycle or half a cycle?

[GM Brazil]

We have this information!

Mostly is like the LiFePO4, it is not good to always use deep discharging. The main difference is that the LiFePO4 have >1000 life cicles and the LiMn have >800. Check the other topic: GM Batteries here, there is a complete description of the cells characteristics: http://goldenmotor.com/SMF/index.php?topic=1373.0

I also found this post on other forum about the cells discharge characteristics: http://www.candlepowerforums.com/vb/showthread.php?s=a94b67858650c6fef8a50379c61c677b&t=234724

They tested these cells and tested again 32 days after the first one.

But I also agree that the LFP on the name creates a lot of confusion, I bought this battery thinking that it was a LiFePO4. The important thing is that GM is a very good quality battery.

[PJames]

One thing I had wondered was why it charged to 42v instead of 45v, now that makes sense that they are LIMn and not  lifepoe4. Still happy with battery,
thanks for the info.

[Leslie]

We have this information!

Mostly is like the LiFePO4, it is not good to always use deep discharging. The main difference is that the LiFePO4 have >1000 life cicles and the LiMn have >800. Check the other topic: GM Batteries here, there is a complete description of the cells characteristics: http://goldenmotor.com/SMF/index.php?topic=1373.0

I also found this post on other forum about the cells discharge characteristics: http://www.candlepowerforums.com/vb/showthread.php?s=a94b67858650c6fef8a50379c61c677b&t=234724

They tested these cells and tested again 32 days after the first one.

But I also agree that the LFP on the name creates a lot of confusion, I bought this battery thinking that it was a LiFePO4. The important thing is that GM is a very good quality battery.

They talk about shelf life of these batteries and I feel that shelf life is relating to a battery on the shelf with no cycles "inactive".

This prompted me to go to google again.

I came up with this hit.

http://www.mpoweruk.com/life.htm

Battery cycle life is defined as the number of complete charge - discharge cycles a battery can perform before its nominal capacity falls below 80% of its initial rated capacity. Lifetimes of 500 to 1200 cycles are typical. The actual ageing process results in a gradual reduction in capacity over time. When a cell reaches its specified lifetime it does not stop working suddenly. The ageing process continues at the same rate as before so that a cell whose capacity had fallen to 80% after 1000 cycles will probably continue working to perhaps 2000 cycles when its effective capacity will have fallen to 60% of its original capacity. There is therefore no need to fear a sudden death when a cell reaches the end of its specified life.

Battery shelf life is the time an inactive battery can be stored before it becomes unusable, usually considered as having only 80% of its initial capacity as above. See also Battery Storage

 
Battery calendar life is the elapsed time before a battery becomes unusable whether it is in active use or inactive as above.

Battery calendar life to my knowledge seems to be a new term touted by battery experts.

Some time ago I was chatting to an EV conversion expert who told me his son kept 500kgs of lead acid up to 12 years only using the car as a towny. 12 freaking years is a good calendar life.

We have not come across such life spans with lithium chemistry as yet but can we speculate if we were to use 80ah Li batteries and drain them to 80% SOC we could expect similar calendar life.

I know SLA shelf life is not as good as a an SLA used with shallow cycles or kept on standby charge.