I have a Piranahmax 4 that draws about .2 amp (manual says .18). I have a 10 pack of aa lithium batteries giving me about 15 volts. I'm not sure on amp hours though.

About how long can I realistically expect the batteries to run?

The piranha is a miser on juice. I used one for several years and it did the job with excellent power usage.

A few thoughts, I am assuming shooting through a hull uses more juice than a suction cup and shooting through the hull over a skid plate will use even more.

Leaving your finder on over really deep water also seems like it would require more juice.

And forgetting to turn it off uses lots of juices as well ;-)

You have the numbers, I can't do the math but somewhere the approximate number of hours are to be found.

My guess.......fishing 1/2 a day you should probably get 10 days out of 10 batteries. Base camping and fishing every day, all day I would bring a spare set.

I've got an Eagle something something. I use 8 AA's and don't even bring extras anymore; we usually go for 4 or 5 nights. I turn it off when I am not staring at it, but it is usually on several hours a day. Color units use lots more juice.

If you're using the finder when on the move, then shutting it down when you find a place to fish for 1/2 hour to an hour, then turning it back on as you paddle.....I agree with Mastertangler and lundojam, the one set of batteries will last 10+ days of fishing. I have the PMax 175, and a single set of 8 batteries seemed to last forever.

Color vs B&W on the head unit is the biggest consideration for battery usage. Depth of water, shooting through hull, has no impact. The ducer is sucking the same power regardless of mhz used.

After that it's just math, assuming you're using regular big box lithiums like Energizers with maybe 2000mAH usable you're looking at 10-12 hours constant usage before the voltage will drop below what the head unit needs.
Unless weight is a huge concern I've been using sealed AGM's for years. For $20 and around 3lbs you can get double the capacity in a relatively compact form factor. The only catch is that sealed AGM's don't like laying on their side and they don't like being left for months discharged.

https://batteryclerk.ca/products/universal-power-ub1250-d5741-12v-5ah-sealed-lead-acid-battery?gclid=CjwKCAjwspHaBRBFEiwA0eM3kQz8gyF_zoJ0z-ZHfR86EXx1vaW6bzTa4VAFq7dYg6bx5M7qQm2hBRoCCwgQAvD_BwE