Hi Charlie,
The battery in Inspiron Duo is not soldered. However, replacing the battery in the duo is not as easy compared to other laptops. It is a field replaceable unit. Please check the manual on the link below for help in replacing the battery.
ftp://ftp.dell.com/Manuals/all-products/esuprt_laptop/esuprt_inspiron_laptop/inspiron-duo_service%20manual_en-us.pdf
Please reply for any further questions.
Thanks and regards
Abhishek B
#iworkfordell