Well.... some PC680 batteries appear to not be the same quality they were in the past. Alot of homebuilt aircraft use them an owners are complaining about the poor service life compared to what they were in the past.

If you can try someone elses battery or try your battery in a similar glider as see how it goes.

There are some devices around that can test the performance of a starter battery in cars. They measure the CCA potential of the battery in a few seconds, perhaps a local auto electrican can do this for you. It only takes a few seconds to do.

Brett