I'm no expert on this Mike but, as I understand it, you can just do the math. A 7 AmpHour battery will operate a device that draws 1 amp for 7 hours. I got a new Humminbird Helix 5 Chirp GPS G2 fishfinder last spring and used it all summer, powered by a 12 A/H battery. The specs say that the current draw for my unit is 600 milliAmps, which is .6 Amps, so my battery should run my ff for 20 hours. However, the stated draw is for maximum backlighting which is the biggest drain on the battery. I turned my backlighting down to 5 (10 is max) and had no problem operating it for about 7-8 hours a day for 4 days on a camping/fishing trip. Also, I had no problem reading it. I don't know what the specified draw is on the bigger unit you're getting but since your screen is maybe 3x the size of mine the lighting draw at maximum backlighting will be considerably higher as well. If you're only using your unit on day trips your 7 A/H battery may be ok but you would probably find a higher rated battery more satisfactory. The fly in the ointment is that as the battery becomes more and more discharged it becomes equally less and less efficient (think of an old car battery) so the math is probably not completely reliable and your real-life operating time will likely be somewhat less than the math would indicate. Tim Percy is the Lowrance guru and seems to always be messing around with his PA and electronics so he'd certainly be a better authority than me.

Just another 2 cents worth from me, my 5" unit is just fine for split screen sonar (2D) & mapping use, which is what I have, but if you'll also have either DI or SI (or both) and you want to use all of the functions together on a triple or quadruple split screen I doubt that you would find the 5" screen big enough. Again, others know better and can chime in on this.

Anyhow, enjoy your new unit - I hope Santa doesn't get that bad boy stuck in the chimney!