Myself for $3 if the battery fixed it you could probably sell it for $100... should take about an hour... not a bad gig.
Supercreep I have a working and a parts Six-Trak, that was my first sequencing DAW in 1983. They still have a great Moog type bass. Great keyboard, you might be able to sell it for parts. Wine Country still services (and buys) Sequentials. http://www.winecountrysequential.com/
It's funny, when you write MIDI Sys Ex code, one of the first things is the manufacturer's ID, it's a number assigned to each company, and Sequential Circuits number is "01". That's because it's owner David Smith pretty much wrote the MIDI code.
In 1984 I had a meeting with John Bowen and we drove everyone so nuts that they all left and we talked for hours about MIDI. John programmed the sounds in the 6-Trak and later did the Korg Wavestation. He was the first Moog clinician in 1973! Another example of how when you meet the real guys at the top that they are regular nice people.