Why will my Latitude D610 only charge some of the time?

I am having trouble getting my Latitude D610 to charge. When I plug in the adapter, it seems to recognize the power source because any "low battery" message disappears. However, the battery light below my screen only comes on sometimes, and the amount of charge (I can see it through "power options" on the control panel) takes forever to change.

This is my second adapter for this laptop; I had to order a new one in July because the old one was not recognized by the computer at all.

Can anyone help?