NiMH batteries in a SPOT-1
I do the same thing with my SPOT-1, run it with high-capacity NiMH rechargeables, but carry a set of Lithiums for just-in-case. An advantage of the '1' is it takes larger AA size, and I have run it for a week tracking 12-14 hrs/day, on a single charge of (2) 2000mAh NiMH batteries. The battery indicator turns red after 24-48 hrs, but I believe that just reflects the 1.2v operating voltage of NiMH. No apparent drop-off of tracking rate - it was consistently 70-80% the entire time.
I believe the 'Lithium-only' is just lawyerly CYA from SPOT. Mine has run flawlessly on a steady diet of rechargeables for almost 2 yrs.
2008 Yamaha WR250R
2007 Triumph Tiger 1050
(... previously ... )
2006 Kawasaki Vulcan 1600 Classic
1978 Honda CB750K