Rebuilt Li-Ion laptop battery questions.

This should be an easy one for the lithium ion battery experts here. I dont know much about them so this is all new to me.

I rebuilt my laptop battery today. The old was made up of nine 18650 type lithium ion cells configured as three series connected sets in parallel. That is three individual cells (2000 Mah x 3) working as a single 6000 Mah cell. Then set up as three of those in series to make the battery.

I changed out the old 2000 Mah cells with new 2800 Mah cells so I have a 8400 Mah battery now.

The first time I put it in the computers charge monitor said it was at 0 charge. It took about 30 minutes to reach 100% charge.
Then I ran it at a normal rate (played a movie) for 92 minutes before the battery was down to 5%. I plugged it back in and now its been charging for 2+ hours and is still only at 42%.

Does the battery need to be exercised some?
And why the slow charge rate now? I dont recall it ever doing that with the old battery pack.
And will the charge monitor circuit in the battery pack have any problem with the larger capacity cells?

Depends on how the charger worked. If it actually metered the current it was putting into the battery it would stop after it let 6000mah worth of current through the battery and think that the pack was full, but the pack now being 8400mah it'd never get full. Also if it was doing a fixed charge rate and looking for a voltage dip as the pack was full the higher capacity pack may cause the voltage change to be slight enough that it can't properly detect the charge state of the pack anymore. Depends too much on the exact method the charger used to detect battery state and manage it.

Where'd you get the new cells from? Some battery surplus suppliers will sell you brand spanking new batteries that are actually old stock, and weather or not they're used Lithium Ion batteries will go bad on the shelf. I'd be a little cautious.