[alanw]

Yes, it's the same for all sizes of 12v batteries. Not sure about your fishfinder but my Lowrance displays the battery voltage on screen, yours probably does as well. It may be a setting you can turn on/off.

Also charge your battery after every use and keep it at 100% all the time for longest life.

Then again, I'm kind of anal about these things. I try and get the most out of my hard earned money. It's just a stupid battery so do whatever you want. The more batteries you guys send to the recycle bin the more lead bullets I can buy cheap