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Old 08 April 2015, 16:24   #1
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Battery Life

I have a 3 metre SIB with a 40 lb. thrust electric O/B and 12v 100 amp/hr deep cycle battery. Performs well to my requirements. The O/B has an integral row of LEDs to show available power. Would fitting a simple ameter or similar be a more reliable and accurate way to monitor? Self confessed electrical duffer. so simple advice please. Ta.

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Old 09 April 2015, 10:49   #2
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Hi
A voltmeter would give you some notion but the drop in voltage wont be linear. That is a fully charged 12V battery off load will be about 12.6V an the same battery flat (or at a point where it needs charging) will be about 12.2V off load. You would see some drop in voltage under load as it discharges but the drop off as it discharges is more like rolling along then falling off a cliff than progressively trundling down a 20 degree slop to the bottom. Your LED indicator is probably only monitoring the top couple of volts.
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Old 09 April 2015, 11:09   #3
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Actually, if you're pulling a lot of current, the voltage indicated at the battery may go well below 12V until the load is removed. I don't know how much a trolling motor pulls, so not sure if that's an issue here or not.

An ammeter is a point-in-time, right this instant measurement, so unless you have some sort of record of how much has been drawn, it isn't going to tell you much. Current drawn depends on throttle setting, supplied voltage, and any resistance in the system; not really sure that would give you any more info than if the motor is turning (which would be obvious anyway - if you get thrust, it's turning; if not, it isn't. If it smokes, you have a different problem.)

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Old 09 April 2015, 11:29   #4
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Yeh. To many variables inc load, temp, internal impedance of the battery itself. Maybe if the motor is used at the same "throttle" setting all the time then the best thing would be some kind of timer to give you an idea where it should be.
You can also buy battery test meters that give an indication of the battery's latent capacity but really as JKY says..............when it stops (and isn't smoking) then the battery's probably flat...........
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Old 14 April 2015, 00:23   #5
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I purchased a simple MinnKota Charge level indicator which has a series of about six LEDs green-red which accutately indicates spent juice by just touching the needle tip on top of the charge indicator on POS and a lead with a clip on the other and it will instantly show how much charge remains. It's small and portable so it can be kept in a tackle box or a case attached to the battery case. I used an older eye-glass case to store it on the side of the battery case. If I remeber correctly, it cost me 25.00 CDN.
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