port battery dies when on a charger? Already killed 3 batteries

[supervetteracer]

I'm killing batteries one at a time and I don't know why. I have a 1989 Trogan 12M MY with Detroit 6 71turbo motors. I can install a brand new battery, sometimes it will be fine, other times it will be dead in a day. I disabled the igntion switches from down below and this seemed to stop it from happening. But yesterday, even with the switches to the ignition off I still lost a battery. Changed it out and then lost another battery the next day. When I test for amperage draw I can switch pupmps, water etc on asnd off fine. When I leave there is no draw on the battery, when I return the battery is dead. And I mean Dead, like ruined. They won't recharge after that. Got any ideas what could cause this to happen? What can I check?

 

[supervetteracer]

How can a battery die from a draw if that battery is on a charger(that works) ? These batteries die hard, like even if I use an old school manual charger they don't come back.

 

[dingbat]

You have a huge current link which shouldn’t be that hard to find. The usual suspects are starters and bilge pumps.

Disconnect the large wire feeding the starters. At battery switch or starter, whichever is easier.

Trim the bilge pump(s) off at switch

 

[alldodge]

Agree, large current draw
Take new Bat measurement with nothing connected, it should read 12.7V
Connect cables, does measurement change at all?

Spit balling here:

Is your bilge wet?

Are you in an area that waves can come in a rock the boat?
I'm thinking maybe a float switch is being turned on by the rocking but then it hangs.

 

[supervetteracer]

You have a huge current link which shouldn’t be that hard to find. The usual suspects are starters and bilge pumps.

Disconnect the large wire feeding the starters. At battery switch or starter, whichever is easier.

Trim the bilge pump(s) off at switch

where would I find a high amperage switch that is capable of handling that big of a load? I'm guessing a regular battery isolator style, like you can get at walmart, won't be enough.

 

[supervetteracer]

Agree, large current draw
Take new Bat measurement with nothing connected, it should read 12.7V
Connect cables, does measurement change at all?

Spit balling here:

Is your bilge wet?

Are you in an area that waves can come in a rock the boat?
I'm thinking maybe a float switch is being turned on by the rocking but then it hangs.

bilge pumps do cycle during the summer months. Guess I'll try changing the pumps and switches.

 

[dingbat]

where would I find a high amperage switch that is capable of handling that big of a load? I'm guessing a regular battery isolator style, like you can get at walmart, won't be enough.

Not sure where you’re going with this.
Typically the starter cable is connected directly to the battery of thru the battery on/off switch.

If the starter(s) is the source of the leak they are shorted internally and must be replaced

 

[alldodge]

Not suggesting to start changing parts, need to find out where the draw is. It's not the pump, if it was the pump most likely a fuse would blow. It might be the switch, but find it and lift it to turn pump on a let it back down slowly to see if it shuts off or hangs

I mention to measure voltage before and after connection to cables because the voltage may drop. If it does drop then there is a current draw, if it stays the same then there might only be a very small drain which would not kill a Bat in a day.

BTW being a boat this large isn't in plugged into shore power?
If on shore power is the Bat charger turned on?