I recently replaced a battery in my c600, and took the existing battery out to use in my c640. In the c600, the battery would never charge more than 80% according to the led's on the battery itself.
When I discharged it and began charging it in my c640, I noticed that it would charge at a much higher rate than the standard battery, but after 5 or 6 minutes it would stop charging. Removing and re-installing pushes it up 4-5 % each time. Then I added a second (smaller) battery in the other compartment that was about 99% charged, and the first battery started charging in a much more regular fashion.
Anybody able to explain this behavior? Is it really OK to use the 5200mah battery instead of the 4460mah 66whr that appears to be standard?
I would conclude that you have probably already resolved this question by this late date in July however, I will toss in my 2 cents for anyone that might benefit.
It might seem simplistic but I would try reversing the two batteries and see what the behavior of the one that never seems to fully charge alone is.
I would also get another known good battery and try it alone and see if it does the same as your problem child did in the main battery bay. See what the lower rated battery does alone in the primary battery bay does. I don't think the solution is in the rating of the battery however.
If there is no change I would live with it by doing as you have to resolve the problem or pay a big troubleshooting bill.
As far as the 5200 mAh battery goes. I don't think you will have any problem with it as far as compatibility goes. If your charging circuits are "gummed" up then you, again, should use the scenario that works as you mentioned.
Talking about “gummed up”, you might also make sure your battery contacts on the battery and computer are clean and tight!
I have a C640 and am purchasing two 5200 mAh batteries, one for each bay. After a long chat with Dell they confirmed that there is no difference between the main battery and the secondary battery. They simply are labeled primary and secondary with unique part numbers apparently since some Latitudes have different physical fits in the secondaries which is not the case in the C640. The electronics of each battery is the same according to them.