lithium battery aging/degradation

[stevo]

As a lithium battery ages/degrades, I assume this means that it will hold less Amp hours (e.g a 10Ah battery when new might only hold 9.1Ah after some time/use). But is there also a decrease in operating voltage? For example, I have a 36V Lithium Polymer battery. Its about 1.5 years old and I have put about 5500km on it (on a Crystalyte 408 using a 20A max controller). When its fully charged (and still attached to the charger) its voltage is 42V. However, I recently noticed that as soon as I unplug the charger, the battery's voltage drops immediately to 40V. Is this normal?

Note: around the same time that I noticed this voltage drop behavior, I had also broken the battery wire. The break was pretty close (ie less than 1/2 inch) to where the wire went into the battery and I didn't feel I had enough room to comfortably solder it so I used a 'butt' connector instead.

 

[dogman dan]

Yes, it's pretty normal, but some batteries may hold the "surface charge" a bit longer. As soon as you touch a throttle, it's gone instantly.

Experts out there, does a batteries internal resistance rise as it ages, and or gets to high cycle numbers? If it does, then the c rate it could handle would drop too.

 

[Russell]

Yes, it's pretty normal, but some batteries may hold the "surface charge" a bit longer. As soon as you touch a throttle, it's gone instantly.

LiFePO4 is the only lithium chemistry I know of with the surface charge you are referring to.

-R

 

[icecube57]

LiMn or the Sony cells used in Bosch pack hold their float forever. The packs I had drop maybe .01v every week. But as soon as you apply a load the surface charge is gone in a few seconds.

My Thundersky pack doesnt hold a surface charge. The cells balance to 3.7v as soon as i take it off the charger they are dropping .01v every 2-3 min until they rest around 3.4-3.5v and not all of them rest equally.