I use SoaringPilot on a M105 since 2 years, and I am very happy with
it.
If you keep the number of SUA data at minimum, the moving map is very
usable (about 2/3 s refresh time with Afterburner at 24MHz). With
cheap disposable batteries, I get about 10 flight hours: more than
sufficient -even for me!- for a 500km task.
For the battery change problem, I have a good solution: get a 3v
button size battery, 2 thin copper blades attached to each side with
insulating tape and inserted behind the battery contacts while
changing the batteries!
I use SP with a small mouse-shaped Deluo GPS, wich is very convenient.

Have a good flight!