My Cranking Battery doesn't seem to be charging when on the water trolling or otherwise,,keep getting a "LOW VOLTAGE" Display on my Depth Finder after a couple of hrs on the water with just the Depth Finder on which runs off the Cranking Battery.The Battery is a little over 3 years old and took it in twice to get it tested recently,but tested Good! Replaced the Stador in 08. Is the Stador the Alternator?