If you're no longer getting the battery lifespan that you need on a full charge, replacing it is the only option. It depends upon what you need from it. One of my laptops has a lower current capacity than yours, but it's okay for me because all I need it to do is to keep the laptop in sleep for a few hours at a time. If you need to work without AC power, you may want more. Parts-People has OEM batteries for that model in stock.
I was wondering when do you guys recommend replacing battery? Notice how the design is almost 50% less than the full charge? I was just thinking maybe I should place an order for a new battery on amazon or ebay but I wanted to run things by you guys... the professions! Here is a snippet of the generated report for Battery capacity history for my Dell Latitude 7390 Laptop:
Recommended Battery Replacement?