Originally Posted by
berudd
Some things in the info the OP provided don't add up.
Says he has a 36v trolling motor but also said "I know two of them are green interstate batteries; bigger than a car battery. Other two are also larger than a car battery but I do not know specifics off top of my head". With a 36v TM, three batteries should be identical and with one, the starting battery, being different.
With 100% certainty, they are not all 4 identical. 2 are black batteries and 2 are green batteries. I checked water levels for batteries when last on boat so I got a good look at color, at least.
He also said: "The batteries are indeed 36v batteries as well" For that to be true, that would mean he has lithium batteries. That would tend to agree with the above statement. You'd know if they are lithiums because they are thousands of dollars instead of hundreds. What kind of TM do you have how much thrust does it make and stated on the head of the motor?
As mentioned earlier, I am running a 112 ft lb Minn Kota Ultex;, 36 volt. The boat originally came with a MinnKota Fortrex 112ft lb 36 volt. I matched specifics when I bought the motor, just changed the model for the spot lock.
I could be wrong on the batteries, I am going off appearance as mentioned. I will be able to verify battery info specifics when I go to boat on Monday.
Not trying to nitpick details but providing good info is how you get good info.
As for your jumper switch, all that likely does is connect to another battery just like jumper cables would.
Yes, it is expected that everything except the TM would be on the starting battery.
Its likely the starting battery that came with your boat is very small, like a Grp 24. For some reason, that seems to be how a lot of bass boats are equipped.
Directly from Nitro boats, the package I bought comes with a "31M-AGM cranking battery upgrade," and after googling this, it shows the green battery my boat has 2 of. Again, without checking specifics in person on my batteries, this is the best info I can give atm.
The fact that the sonar units won't power on while the lights and pumps still run is expected. The units have a minimum voltage requirement and won't come on if that is not met. Lights and pumps will still run they will just be dimmer and slower, respectively.
Batteries don't last forever. Either between chargers or over longer period of times. If you frequently spend 18 hours on the water then you have been discharging the battery very, very low each time. That is hard on batteries and shortens their life span. So, it would not be surprising that what might have worked before not longer does. You killed your battery.
For your use case, I'd recommend a house battery. You won't need another battery, just re-purpose the 4th battery you already have. You'll need to do some rewiring but basically you want a battery that is dedicated to electronics and and other accessories such as lights and pumps. This means your cranking battery to only has to start the motor. It will sit there unused, without being discharged, until you need it so it will probably be good for days or weeks like this. The house battery will need to be charged however.