One battery losing power

[Middleschoolnarc]

Hello friends,
I have a pontoon boat that is powered by a Torqueedo 4.0 on a 48 volt battery system.
My trip on the water is been cut short due to loosing power on one battery.
When I test the other 3 batteries I still have 12 volts on them but the one that ends up connected to the power switch inside the battery compartment is down to 6 volts?
Can someone help?
Thank you

 

[sam am I]

Assuming all the battery's are good and equal'ish in capacity?.......Sounds like how your toon is wired, the 48V that is needed to run the motor is made up of a series 4-12V batts? The manu then has tapped off (and switched) 1 of 4 12V batts to run 12V to run dash stuff, like stereo, lights etc?

Which of course is taking down just that batt much faster, In order to draw them ALL down mostly equal (and like golf carts do), you need a 48V to 12V converter, so you can run the 12V stuff off the entire bank of 4 and not just 1 of 4.

Amazon.com

Victron is pretty good stuff and FWIW, I currently have 3 or 4 of their products(inverter, several diode iso's, smart shunt) and so far so good.

 

[Middleschoolnarc]

thank you for your reply.
There are no auxiliaries attached to the loser, I even switched battery and still the drain occurs.
The only wire is the positive attached to the on off switch.

 

[sam am I]

So, as I mentioned above, if it's the same capacity as the others, must be bad battery then eh?

 

[Middleschoolnarc]

Thank you for your response,
There is nothing wired to this battery the positive only goes to the on and off switch, the other batter has the wiring for auxiliaries that is steady at 11 to 12 volts. I also have switched battery and does not solve the problem.

So, as I mentioned above, if it's the same capacity as the others, must be bad battery then eh?

I have changed the battery but same problem with other battery

 

[sam am I]

Hmmmm, I guess I'd have to be there to look at it. However, there HAS to be a current draw on that specific battery when it's in that specific position relative to the others, right? Something electrically has to be different about that position in the line-up....Same size, same capacity, same age series config'd batteries typically discharge all around the same rate unless one has more of a load then the others...No real magic happens

 

[dingbat]

When was the last time the batteries loaded tested?

Disconnect the batteries from each other and test independently.

A fully charged 12 volt battery should measure roughly 12.7 volts. A battery is considered dead at 12 volts

 

[JASinIL2006]

Deleted. Replied to wrong thread.

 

[Middleschoolnarc]

I have tested the batteries they are roughly 12.7 volts. But if I take the pontoon out only the battery that is connected to the on off switch drains down to 8 or so . When charged the full loop of the 4 batteries is 52 volts
There is no other wires hook up to the battery, I have switched batteries and the same happens.

 

[dingbat]

I have tested the batteries they are roughly 12.7 volts. But if I take the pontoon out only the battery that is connected to the on off switch drains down to 8 or so . When charged the full loop of the 4 batteries is 52 volts
There is no other wires hook up to the battery, I have switched batteries and the same happens.

Power (+)from battery #1
Ground (-) from battery #4

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https://assets.discoverbattery.com/documents/09_discover-general/885_product_application_literature/gui-battery-banks-connections-configurations.pdf