Good morning guys,

Question, my boat has twin Rule 1100GPM bilge pumps in it and they utilize Rules water sensor not a float switch design. Last season rain water built up on the boat in 1 very heavy storm, the 1st pump didn't activate and the 2nd enough water made it to the sensor but not enough for the pump to actually pump water and shut down so it killed one of the two batteries.

I check my boat during and after every heavy rain fall and it was fine but this season I want to add a battery tender to it. Im in a lake so its fresh water but can having a tender aid in electrolysis and attacking the drive? I mean my assumption is it would be the same has a boat being plugged into dock power but I want to see if Im overthinking this.
https://www.batterytender.com/6-amp-onboard-charger

Are you going to be using the tender on its own extension cord? or will you have shore power hooked up and then tender plugged into the boats outlet somewhere?
Either way i don't think it matters as the chargers usually use transformers to convert the power to 12v and there is no direct AC power contact to the DC power output. So unless there's a short somewhere and somehow feeding AC power into the DC circuit i don't see any electrolysis issues going on. If you already had electrolysis before hand this shouldn't make it worse

You should never use an automotive battery charger on a boat that is sitting in the water. Marine battery chargers have floating grounds that isolate the battery's negative from the AC sources neutral. This is done to prevent electrolysis that can very quickly dissolve metal underwater fittings and sink your boat. I've seen it happen a number of times and it can even impact boats docked next to you. If you want to use the automotive charger then disconnect the negative battery cables before hooking up the charger.

GF?

Where can someone find this?

A Mercury QUICKSILVER isolator prevents this sort of corrosion. I really need to get one; when I go to Tablerock I'll keep my boat in a wet slip for about a week at a time, and the shiny stainless steel prop becomes totally calcified, as does the black outdrive....and it takes something like CLR to get it off.

So the first pump didn`t activate and the second not enough water made it to the sensor to pump water ...so how did it kill the battery when neither pump worked , I`m confused.

For $25 more. You can buy a Promariner ProSport and be done with it.

Sounds to me that the sensor for the second pump was mounted at the wrong height and the pump turned on but didnt actually pump anything so it kept going and killed the batts....

First pump didn't activate, the 2nd did but water wasn't deep enough for the pump to suck and it just ran doing nothing. I will address these issues but I want a tender on the boat to ensure my batteries are always topped off. Batterytender makes a marine tender I was going to get not just one for a car.

Eaxactly what happened, the pump wasn't flat at the base of the hull, it was on the v with the sensor facing downward. This since has been addressed.