At 80% it will trickle charge if you leave it on. Have you enabled showing percentage on the status bar (Battery > Visual Settings > Battery Display Styles)?
Also make sure you haven't set it to schedule charge or it will slow right down until the schedule time, similarly with slow charge option.
Are you using the original charging block?
Your battery, if limited to 80%, will never really charge to full. I use the same and the max it goes to is 81%.
