I use ultra low discharge batteries in my Tiger Shark. They store forever with a full charge, and don't have the discharge failures like so many other high capacity rechargeable batteries. They're made by Maha, and called Immedion. Eneloop is another brand, but they cost more at the time I bought these.
The problem that I found with high capacity rechargeable batteries is that when you get them brand new, and fully charge them, they let you detect longer. But stick them on the shelf for a couple of months, whether using them or not, and you'll find that they don't keep their capacity like they did in the beginning, nor will they ever reach that higher point of capacity anymore. Typically, the higher the cap, the faster the idle discharge rate when not in use.
These low discharge batteries are the ones you see in the store that are rechargeable, but state that you don't have the charge them the first time that you use them. That's because they can hold up to 80 and 90% of their charge over the course of sitting on the shelf for a year. Try that with your average rechargeable battery.
Also consider this. If you need 8 batteries, at 1.5 volts, you're at 12 volts with alkaline. If you do this with your typical rechargeable battery, they're at 1.2 volts, which is a loss of .3 volts per cell, making 2.4 volt loss over those 8 cells, leaving you with 9.6 volts to run your equipment. Make sure that you can do that by checking with your mfg.
For me, Tesoro states "This should not affect your depth and sensitivity, it but will affect the time that you are able to hunt". I have two packs of batteries with me at any time. The first pack is my Immedions, and the second is a pack of Duracell or Energizers. I've never had to grab the second pack on any daily hunt I've done, in the water or out, and primarily using my clean sweep in the water.
my2c
Ohiotech