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.

[ranger098]

So last night i headed to the boat with the multimeter and spare battery. The starting battery read 8.6 and aux battery read 11.8. Jumped the boat and both batts read 13 something while running. ran around for like an hour, shut the boat off and both batts read 12.5. Checked them again this morning and the starting battery read 12.5 still, aux battery was 11.8. going to check it again when i am done with work.

Still not sure what the issue is, but monitoring the hell out of the batteries will help troubleshoot. I also think there's somthing i can do to confirm a slow draw, disconnect the ground and put the MM inbetween the batt ground and the cable, if theres amps being drawn then i have a slow draw. Maybe ill try that

[MLA]

Here are some things learned:

Both batteries were depleted
Batteries are indeed isolated from each other since they had a different at rest voltage level
Alternator is charging and both batteries are seeing that charge, so again, the isolator is working
No parasitic draws on main cranking as it held at 12.5

Going from 12.5 to 11.8 overnight, may indicate a small parasitic draw on the house battery, but does not explain why the main cranking was down to 8.6V

If your meter has the capability of measuring current draw, that will tell you for sure, that there is or isnt an unwanted draw.

Im more concerned about the main cranking showing 8.6 but then holding 12.5 over night.

[ranger098]

I too am confused on the 8.6, i am thinking either theres a parasitic draw from something, or the battery is shot. I am not 100% sure the main battery is solely for starting, the bilge and maybe some other factory things may still run off it. I know the radio and amp are on the other tho. The research will continue in a few hours and over the weekend.

[rje-3]

I know with my factory dual battery setup the bilge pump is not affected by the battery isolator switch. In fact, I even pulled the bilge pump circuit breaker with the battery isolator showing off and the bilge pump still kicked on. If your setup is like mine and the bilge pump is draining the battery, you might have to disconnect the battery cables to stop the pump from running. Of course that could cause other problems for you, but it might be worth trying to see if it is the bilge pump causing the battery drain issue.

[zabooda]

The batteries needs a load test at an automotive parts store. A weak battery will maintain 12 volts by design without a load. there appears to be more than one issue here and having good batteries may eliminate some of the other issues.

[ranger098]

The batteries needs a load test at an automotive parts store. A weak battery will maintain 12 volts by design without a load. there appears to be more than one issue here and having good batteries may eliminate some of the other issues.

Update to anyone interested, I think it may just be the battery naturally losing charge, and it may need to be replaced. I was unable to detect a parasitic draw with the MM, and the battery dropped from 12.6 to 12.09 in just over 24 hours. I ran it all weekend (fri sat and sun) and it worked great, but if the boat sits for 5-6 days during the week the battery just loses too much charge.

I also theorize that running of the bilge draws from the starting battery and since it's on its way out, a few minutes of bilge running may bring the current level way down. Im going to leave it at that for now, and probably just drop the $$ on two brand new optimas for next year. Thanks all