solotripper wrote on Jul 29^th, 2014 at 1:42pm:

I also bought 12 Panasonic Eneloop Lithuim batteries and a nice charger.

Solotripper
I did not know Eneloop had Lithium or rechargeable Lithium batteries.  Where did you buy them?
I could not see any improvement in my detector performance above 10 volts.  I did see the unit drew more current the higher the voltage went.  So from what I was able to measure if you use more than the correct number of batteries they will last less time. If you do less batteries than the optimum number they will power your detector correctly for less time although they will still have considerable power left in them it will be at too low of voltage to properly operate the detector.
For non-rechargeable batteries I recommend 8 maybe 9 but not 10 Lithium batteries in series.  8 will give you the most hours of operation for the buck and will out last 10.
If you are using Alkaline I recommend 10 in series. I have had better results with Duracell batteries than any other Alkaline.  Duracell also sell a Duracell Quantum which has 33% more power than regular Duracell.  Costco sells both Duracell 2022 (regular Alkaline) and there Duracell Quantum. 
Most rechargeable batteries ( NiMH or NiCad) are lower voltage than the non-rechargeable so they require 10 batteries in series.  I have never tested the kind you bought.  Can you measure the output voltage of your 10 pack? Your fish detector may have a voltage readout if you do not have a meter.
EDIT
Just thought of something did you get Li-Ion or LiFePO4 batteries?  If you did do not connect 8 or 10 of those to your detector.  They are 3.7 or 3.2 volts and you only need 3 or 4 of them.  They also need a protection circuit to prevent over charge and discharge.