Wlfdg... the guys above are on the money... but I'd like to add one more word of caution... not all calls can use the lithium batteries. I have a foxpro spitfire and it won't run on them... though my fusion does (the fusion actually has a setting on the ecaller to change from alkaline, nimh, lith etc)... but it uses twice the batteries and really sucks em down.
The spitfire I can use 3 nights back to back.... the fusion... 1 night, so if I were you, I'd try to stay with a call that will use lithiums... but isn't a battery hog. That would be the way I'd go if I had to do it all over again.
Good luck buddy... and hope to see some of your mutts posted soon!