Dell Inspiron 1520 battery not charging, but the computer says it is charging normally

My service tag is 9H90JD1 and I bought it Aug 25 2007, so the battery warranty and the product service warranty are expired. I use the battery power on my Inspiron 1520 only sparingly. For the most part, I keep it plugged in. Apart from the current situation, I have never allowed the battery to fully discharge. About 2 weeks ago, I took the battery out to see if the laptop would run on the charger power alone. It did, but when I re-attached the battery, the battery indicator light started flashing red and blue. The battery was at about 100% at that point. When I disconnected the charger, the battery drained as usual, but when I plugged in the charger again, the battery no longer charges. I included a screen shot of my battery health message that says the battery is able to charge normally even though the battery charge no longer increases even with when the laptop is powered down. I also tried to follow Dell troubleshooting tips, but when trying to run the BIOS program, I get the message "The battery must be charged above 10% before the system BIOS can be flashed"... of course, if my battery COULD charge above 10% I would not be having this problem.

Please let me know if there is anything I can do to fix this. If not, does anyone know of a decent site to get a reliable and cheap replacement? I really don't want to pay $135 to Dell for another battery that will only last about a year. I'm a poor college student trying to plan a wedding and can't afford random extra expenses for a battery product that is clearly sub-par based on all the other comments I have read. I think it is absolutely ridiculous that Dell manufactures a battery that just barely outlasts its special warranty. Any help would be appreciated.