Thanks Steve, I guess what I was asking is can I add the $118 unit to what I already have, battery, case, etc.
I don't see why the battery would be a problem unless you're referring to the compatibility of the power cable to the new Piranahmax head unit. Regarding that cable, the transducer and the mount, it's hard to say whether these would be backwards-compatible with your older unit. I would guess not, since most companies now build "planned obsolescence" into their business models and, as such, do what they can to force you to buy new stuff.