Battery Isolator Question

[ranger098]

This may be a dumb question, but i gotta ask. my dual battery setup uses an isolator to keep them charged. lately my batteries have been dead when i get to my boat and it really sucks. I suspect the bilge kicking on and draining my battery (working on getting the cover just right to avoid pooling after rain) but its weird that both batteries are dead.

I do have the battery grounds connected to each other, could that be causing the batteries to work together instead of separate? There's no great ground where my batteries live (under the glove box) so i connected the aux battery ground to the engine battery ground. positive wires are separate though.

[sivs1]

post a few pics of your setup, you may just be on a switch and if 1 and 2 is selected both will drain. if you run the engine with only 1 selected you are only charging that battery. I am sure your setup is similar to mine unless there has been some type of mod done.

[MLA]

Does your dual battery setup w/iso also use a manual switch? Are you turning the switch off when the boat is stored? 99 of a 100 setups, it is appropriate to have the house battery GND connected to the main battery GND post.

[ranger098]

I know for sure that i have an isolator and do not have a selector switch. If the grounds are OK connected together, and i thought they were, then i need to ensure that all accessories are on the 2nd battery. Ill be playing more with it tonight after work... good thing i have a 3rd battery to keep things going or id be alot more pissed!

[MLA]

Even the main boat systems can be a parasitic draw on the cranking battery over time. With no switch, theres no way to isolate the loads from the battery. Your isolator likely keeps the banks separated from each's loads.

You also need to know the condition of the batteries and what their state of charge is when the boat is put away. It may appear that they are dead when you come back, but its possible that they are low when you walk away.

[rbeckner27]

I installed a true isolator on my mojo with two batteries and was experiencing the exact same problem with batteries being drained so I pulled it out and have just wired in parallel without any issues whatsoever. Now I understand that it doesn't help me with idea for two separate systems but we don't regularly sit and listen to music for long periods of time.

[ranger098]

I installed a true isolator on my mojo with two batteries and was experiencing the exact same problem with batteries being drained so I pulled it out and have just wired in parallel without any issues whatsoever. Now I understand that it doesn't help me with idea for two separate systems but we don't regularly sit and listen to music for long periods of time.

Hmm that's interesting. I think i could easily test this my taking the wire that charges the 2nd battery off and running a short wire from the 1st battery + to the 2nd battery + and see if my issue is resolved.... not a bad thought. I also am going to take both batts out and give em a good bench charge.

It's weird that this just started happening the last 2 times i went out.. they both were perfect all summer until last week. Sumpm's up.

[zabooda]

I take it you have two identical batteries and purchased the same time. Without an isolator, your battery is only as good as the weakest battery as that one will behave much like a load rather than a battery. If you are looking for electrical drains then you should insert an ammeter and isolate the source.

[ranger098]

I take it you have two identical batteries and purchased the same time. Without an isolator, your battery is only as good as the weakest battery as that one will behave much like a load rather than a battery. If you are looking for electrical drains then you should insert an ammeter and isolate the source.

I definitely do not have two identical batteries, and the aux battery is debatably bad (stinger that was rebuilt). But because I have an isolator wouldn't that keep the starting batter safe?

[zabooda]

Your isolator device may be suspect. What type isolator do you have? I would temporarily move to one battery and move all your wires over to it and see if the condition improves. You still may have some parasitic power drain that you may need to trace.