Battery life question

I just treated my self to a Lowrance Elite-5 Fishfinder/Chartplotter  http://www.lowrance.com/Products/Marine/Elite-Series/Elite-5/

I have a Cabela's 12V 8amp battery.  I tried it out last weekend and found that setting it at full brightness (10 setting) was best for me.  I am usually at the Sonar Page about 70% of the time and 30% on the GPS page.

I was wondering how many hours I can get out of it?

That is a question similiar to asking how many licks to the center of a toostie pop. You won't really know till you lick it all the way down.     . I had the same one myself this year but it was stolen after the first day I used it.    . Most finders will show the volts left on the battery and it will depend on how many cycles your battery has been charged. I think.

Mel, I can't find any info on that unit regarding how much it draws, but if you really want to find out, you can bring your setup over to my place. I have a couple of meters that can tell you exactly how much it draws. Beware that batteries usually do not put out what they're rated at. If you want to know about the battery's true capacity, you'll need to put it on a smart charger that has a Test mode, let it drain at the rate that matches the draw of your ff. Or, simply run your setup the next couple times you're on the water to see how long it lasts.

Mel, I can't find any info on that unit regarding how much it draws, but if you really want to find out, you can bring your setup over to my place. I have a couple of meters that can tell you exactly how much it draws. Beware that batteries usually do not put out what they're rated at. If you want to know about the battery's true capacity, you'll need to put it on a smart charger that has a Test mode, let it drain at the rate that matches the draw of your ff. Or, simply run your setup the next couple times you're on the water to see how long it lasts.

Ernest - I will try your advice on running the battery.  I will set it at half sonar and GPS setting at home and set a timer.  I assume this is not bad for it and creates the most power demand.

My Cabela's 12V 8amp battery is like the Energizer Bunny.  I had the unit on at full brightness, GPS / Sonar split screen for 8 hours last night and was still going.  I turned it off because I had to go bed.  Pretty good for a $20 battery.
http://www.cabelas.com/sonar-accessories-cabelas-rechargeable-12-volt-battery-1.shtml