While adding water temp to the screen overlay on my Lowrance Elite 5 I found some other items available that included the system voltage Now I have a digital readout for my battery voltage to keep an eye on instead of the 4 green lights on my trolling motor. Since I'm using one battery for everything this is a critical measurement for when I need to quit using the TM and still be able to crank the 90HP engine. I have watched the voltage drop to 11 with the 55lb TM on high and it will come back up to over 12 with it off. I let the no load voltage get to 11.9 the other day with no problem, but I'm thinking the full load voltage is a better indicator of how much juice is left in the battery. What do you think?
I think it's a matter of time before you are going to be calling sea tow! Voltage isn't the only concern if your amperage drops low enough you could have enough volts but the engine still won't turn over fast enough to crank. Also depending on your engine some motors ECU cut themselves off if voltage drops under cranking load might be turning over but it won't ever start! Be careful running one battery on such a large engine and trolling motor.
First, for every 5% below 50% of battery charge you go you shorten the life of the battery by 50%. The good news is that I have yet to see a fish finder that did not display the voltage .5V lower than what you would measure at the battery. As Creek said some motors will not start if the voltage drops below 11V while cranking. Not sure what size battery you are using but if starting with measured at the battery voltage is less that 12.1 it is not hard to fall below 11V's. The larger the battery (provided it is in good condition) the more wiggle room there is. Voltage is important down to the .1V
Thanks for the responses. CR I have a Sea Tow membership for when the time comes. CJ I'll check my battery terminal voltage vs my Lowrance to see if its off. .5V is like 50% of the battery charge per your chart. If mine is off .5V I haven't fallen below 90% battery charge. Most of my TM use is at level 3 or 4 where system voltage drops around .2V. Its at 10 where the voltage drops around 1V.. As best I can tell the boat was originally set-up with a small AGM battery from BPS for the TM and a size 24 for everything else. I went with one dual purpose marine 27M that according to specs holds the same amount of juice as the two I replaced, weighs 10 pounds less, and frees up space in my console. If all else fails I've got the manual starting rope, a push pole and a SeaTow membership.
You are right on that voltage difference between the depth finder and the battery. Voltmeter on battery measures 12.6 while depth finder shows 12.1 at full charge. With battery charger on, voltmeter shows 13.7 at battery and depth finder shows 13.2. I'll be keeping a close eye on the voltage for sure.
