If the battery, without a load, after fully charging, only puts out 11.45 Volts, it is dead... The plates are likely sulphated. A good battery should read 12.7 Volts, at rest. You can go with another lead-acid, or put an AGM in there. The AGM's are sealed, no maintenance, work at any position, cost more, but last 5+ years.
There is a brand called
Moto-Batt, yellow in color, which has universal posts, is AGM, and can be had for a reasonable price. Check e-Bay for the seller, based in Florida. He seems to have the best price, and a wide variety of sizes. I found an article comparing motorcycle batteries, on the Internet, and this brand won out in the tests, over all the other five, or so, brands the author tested. When my lead-acid's go, this is what I plan to install. Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII