Humminbird 141c; battery?

Went to radio shack last night and then went crosseyed.

I can't find my installation guide, but I think it calls for a 12v battery...

RS had lead acid and lantern 12v batteries. The lantern battery was less than $10 while the lead acid was $35. What should I use? Who sells the cheapest?

Either or neither

Both would work (pretty much all FF's are 12V), but you'd probably druther not have a wet lead acid battery ($35) as upside down happens and acid is hard on your complexion. The lantern battery would be fine too, but it's not rechargeable (is it?).
Most folk use a 12V 7 amp-hour gel cell battery ($20 to $40 depending on where you buy it). They are variously known as deer feeder batteries, alarm system backup batteries,,,,
The last one I bought was from Fisherman's Marine (deer feeder bat) and it was $25
I use a trickle charger from Harbor Fright ($7-$12) but a lot of people like other chargers better. Mine works for me just fine though.

Radio shack is where i got mine 6 years ago and I am still using the same one. It is a lead acid 12v battery that is sealed so it does not leak. Used for alarm sysetem back ups. also you might think about the battery that you get at toys r us or walmart for those kids jeeps that they ride in. they come 12 and 6v. just have to rig it up some way to plug in. maybe get an old kids jeep some where and strip the parts out of it.