Lithium questions

[JimmerG]

I'm sure this has been discussed a million times but I can't find it anywhere.

There's lots of talk about NiMh cells and their inherent self discharge over the months. I use protected Trustfire 18650s for a bike light - do these have a self discharge rate?

I only really use this light once a month - would I be better off storing the cells at half capacity and then charging them to full just before I use them. Or if I store them at full capacity for a month would it be necessary to top them up just before use?

Thanks in advance for any help.

J

 

[Oddjob]

According to what I have read, good quality lithium ion cells hold their charge for quite a while, a year or more IIRC. I don't think it would be a problem to let them sit for a few months. Regular NiMh cells loose their charge but low self discharge NiMh like Eneloops hold their charge for quite a while.

 

[drmaxx]

Here's a good answer:
http://www.batteryuniversity.com/partone-19.htm
Cheers

 

[JimmerG]

Thanks for this info guys - my ponderings have been perfectly answered

J

 

[brighterisbetter]

On March 24, 2005 I charged an unprotected 18650 Li-Ion cell up to 4.000 volts and placed it in room temperature storage. A few hours later it was at 3.989 volts.

On March 26, 2005 it was at 3.976 volts.

On May 14, 2005 it was at 3.975 volts.

On October 1, 2005 it was at 3.974 volts.

On December 11, 2005 it was at 3.973 volts.

On February 10, 2006 it was at 3.973 volts.

On March 2, 2006 it was at 3.973 volts.

On April 19, 2006 it is at 3.973 volts.

Not much in the way of self discharge...

EDIT: I tested this cell for remaining capacity, then charged it back up to 4.000 volts and checked the capacity again. After 1 year of room temperature storage, this cell had 95% of its original capacity. END EDIT

Tom