I may get a chance to repeat the measurement with the transducer in the neighbor’s swimming pool.
These fish detectors are designed to go in a boat with a 12 volt battery.  A 12 volt battery on a charger will measure up to 16.2 volts.  Under a light load and not being charged it will measure 14 to 15 volts (Ya I know a 12 volt car battery has 14 to 16 volts).   So these fish detectors are designed to work best on 14 to 16 volts although they will work somewhat down to about 8 volts. Alkaline batteries new measure 1.6V and drop to about 1.4 volts with little use and when 80% of the energy is used the voltage will be 1.15V. If 10 AA Alkaline batteries are connected in series the voltage will start at 16 volts and when 80% of the energy is used up the voltage will be 11.5V.  New Lithium AA batteries measure 1.82V and drop to 1.5V with little use and when 80% of the energy is used up the voltage will be about 1.38V.  If 9 AA Lithium batteries are connected in series the voltage will start at 16.4V and when 80% of the energy is used up the voltage will be about 12.4V.

I was wondering about that. One year I borrowed one and got the long life lithium. Stopped at a campsite for a late lunch, decided to stay, no evening paddle, flipped the canoe over for the night.

Next morning the batteries were dead. I assume I left it on but I do remember it had a light and I think that was off so I don't know if the light had anything to do with it or if ~15 hours of pinging the moon on auto depth sucks more juice.

Last trip I used a different one and easily used it 15 hours the last two days of an 11 day trip. I'll take a wild guess and say I had it on for ~50 hours that trip. Same set of the lithium whatevers was still showing over 12 volts in 199 feet of water on my way out as I recall.

I think the most value from this type of data is to make comparison with other detectors.  I do not have any other to measure now.  But in as much as you asked I went to the Duracell site and looked at the AA ULTRA and Copper Top batteries.  By using the average of the average currents over the usable voltage range and assuming I had 10 batteries in series so I could use the batteries down to 1.1 volts I get between 9 and 13 hours of life.  In actual use I get better than that more like 20+ hours.  The reason for the difference may be the unit draws less power when it is not searching for the bottom like it is hanging up side down in my garage and I use the batteries to a lower level than 1.1 volts.

Hey Magic, can you translate that into simple English? Zog much interested but no understand much beyond volts.

Are we talking 8 AAs or what?

For those who may have a need to know
Eagle fish Mark 320 current draw. Voltage is
power supply meter with a fluke multimeter
in series to measure the current. Transducer is
glued to bottom of canoe not in the water.
Volts      Imin      Imax      Iave
8      84ma      332ma      104ma
9      88ma      372ma      111ma      
10      88ma      456ma      116ma      
11      92ma      476ma      121ma
12      92ma      476ma      131ma
13      96ma      612ma      132ma
14      96ma      448ma      136ma
15      100ma      492ma      141ma
16      100ma      532ma      148ma
17      104ma      560ma      153ma
This unit works well when supplied with 12 to 16 volts.