Battery Charging Issue Related to BIM only?

[bilmet01]

Hi Folks, could use some help with a charging issue. I bought a 2015 Forester MBS 2401S from my local dealer near end of this past summer. Had a few 4/5 night trips with it and was noticing my battery monitor never showed house batteries ( 2 Optima Blue D34M AGMs ) fully charged even though I was plugged into shore power most of time?

The dealer had given me a "30 day warranty" on everything working ok so I went back to them with a short list including my questioning if charging system is working correctly. They checked charging system and identified issue with BIM ( battery isolator manager ? ). Currently waiting for part to come in ( now 10 weeks and counting ) but that is another issue :-(.

In mean time, I read the following on function of BIM: connects 2 battery systems together during charging. Coach batteries charged while driving and chassis battery charged while plugged into shore power ( I assume while generator is running as well ).

So it make sense to me about the house batteries not being charged by the MBS alternator as I while waiting for the part I have taken my RV for a 25 minute drive from the dealer lot and did not see evidence of house batteries being charged ( using my new voltmeter instead of just control panel monitor ) but I question I do not have an additional issue with my batteries?

The reason being I have twice first checked the voltage on my batteries at being about 11.7 V , run my generator for about 45 - 60 min with reading then at about 12.2 ( knowing that is a false reading right after charging ) and then next time I run my test within week or two I see voltage of batteries back at about 11.7 ( 1/3 full based on control panel ) . I have made sure the battery disconnect switch was turned off when leaving the RV. Also confirmed voltmeter showing 14.2 V while generator running.

What I am hoping someone could confirm for me that if this does sound more than just a BIM issue? I assume the dealer should be able to confirm the state of my batteries too ( if they have not already done so ) but was hoping to get someone's opinion before I try to talk to the technician who diagnosed the issue ( service desk person does not seem to be familar with the issue ). Would appreciate any input. Thx.

Note: I have also read on this forum that my 2 Optima Blue D34Ms are not true deep cycle batteries so I had planned to replace them eventually but just wanted to understand if I should do that sooner than later.

[Reverse_snowbird]

Originally Posted by bilmet01

I have made sure the battery disconnect switch was turned off when leaving the RV.

Which battery disconnect switch are you using... the one inside the rig or one on top of the house batteries? If you are camping and plugged into electric, I think the battery disconnect in the rig has to be 'on' to charge the house batteries.
You have AGM batteries which usually take a longer time to recharge. While driving you may more time to recharge the house batteries.

Unless you are using a battery disconnect switch on the batteries themselves, you're going to get a 'parasitic drain' on the batteries. You can also disconnect the negative cable on the battery which will stop the drain.

[bilmet01]

The battery disconnect I referred to is the knob on the inside. I have kept that on while camping or charging at home. It has been only switched off while not using camper as well as sitting at the dealer.

I just wanted to emphasize that I have had the camper plugged in to shore power the night before heading out and then a few days plugged in at campsite only to find batteries not fully charged after getting home ( just an hour away ). That is why I am questioning the actual batteries and not just the BIM operation?

Unfortunately my RV is at dealer currently and I cannot plug it into shore power right now to confirm cannot get batteries to 100% charged. I could only try running generator for a while which does not seem to me to be helping? I believe my PD9260C converter/charger is working fine based on seeing 14.2 volts on the batteries while generator is running.

[bilmet01]

Any other input I could get concerning this? If not, I guess I will be at the mercy of the dealership's diagnosis. :-( Probably will try to talk in person with the technician who determined a faulty BIM to hopefully better understand.

[BehindBars]

There are variations in available battery state-of-charge voltage charts, and temperature also comes in to play, but I think most would agree that 11.7 volts measured at the battery indicates a severely discharged battery. If the batteries have frequently visited this low charge level or lower, they may be destroyed by now. You may not be able to do more troubleshooting of the charging system until you get some known good batteries in place.

Forum member TowPro did some research on BIM operation and wrote up extensive details in a few posts, which is worth a read. Part 1:
https://www.forestriverforums.com/fo...-a-194290.html

[bilmet01]

Thanks. I thought not being able to get my batteries above 11.7 V after running the generator a couple of times at the dealership is not a good sign. As well as not seeing fully charged batteries after being plugged into shore power a few days at a time for some short trips in Aug-Oct. :-(

Since the dealer tech diagnosed needing a new BIM for me ( free of charge with my 30 dealer warranty ) I will let them go ahead with that install but I am still planning on running the battery strength question by the tech as soon as I can. I would assume they can easily test the batteries for me to verify I need new batteries too. Might be too much they want to analyze for me for free. :-)

I will start looking into new true deep cycle batteries which I figured I would should get anyway. I have already read a lot of threads on the forum about battery recommendations. Would like to have considered golf cart batteries but do not believe they will fit in my step compartment. :-(

Thanks so much to Behindbars and ReverseSnowbird for your input!

[bilmet01]

Update to my issue:

My dealer did finally get the new BIM for me in January and installed it. So I though I was all set but took my cover off today and using my voltmeter I confirmed the house batteries are still not being charged by my alternator with the engine running so it does not look to me that they fixed the problem. :-(

I searched the forums and found a similar issue posted in 2018 with this reply:

"You have a bad or non functioning isolation relay.

Start the engine and while monitoring the house voltage with a digital volt meter, push and hold the boost switch.

If the volts go up, there is a isolation control issue. If they don't, its a solenoid issue.

To find the solenoid, have someone push the boost switch on and off and listen for it."

Can anyone confirm for me this would appy to my 2015 Forester MBS? I am not aware of a location of a "boost" switch or if I have one? If this applies then could they have repaced the BIM but actually needed a new solenoid?

[bubbles]

Originally Posted by bilmet01

Update to my issue:

My dealer did finally get the new BIM for me in January and installed it. So I though I was all set but took my cover off today and using my voltmeter I confirmed the house batteries are still not being charged by my alternator with the engine running so it does not look to me that they fixed the problem. :-(

I searched the forums and found a similar issue posted in 2018 with this reply:

"You have a bad or non functioning isolation relay.

Start the engine and while monitoring the house voltage with a digital volt meter, push and hold the boost switch.

If the volts go up, there is a isolation control issue. If they don't, its a solenoid issue.

To find the solenoid, have someone push the boost switch on and off and listen for it."

Can anyone confirm for me this would appy to my 2015 Forester MBS? I am not aware of a location of a "boost" switch or if I have one? If this applies then could they have repaced the BIM but actually needed a new solenoid?

I think there are 2 BIM's out there one that does use an external solenoid to interconnect the chassis and coach batteries and another (newer) BIM that does not use an external solenoid and instead interconnect is within the BIM. You don't have to start the engine to see if the BIM with the external solenoid is energizing; just actuate the emergency start switch (if you have one) and the solenoid should energize. You should hear it. Of course for charging if you start the engine and check the voltage at the coach batteries it should be roughly between 13 and 14 Vdc indicating the solenoid (BIM) has energized. With just shore power (ignition OFF) applied the voltage reading at the chassis battery should be above 13 Vdc.

[bilmet01]

Also, just wanted to confirm that I do see the chassis battery being charged ( 14.2 volts on voltmeter ) while the engine is running.

[bilmet01]

Thanks for replying so quick Bubbles! Not sure what type of BIM they replaced but I can confirm that with engine running my voltmeter is currently at 11.5 ( got a battery issue to fix as well ) while I see 14.2 volts on chassis battery. I have also confirmed that my house batteries are being charged ( seeing 14.2 volts ) when engine is off and hooked up to shore power. Telling me my house converter/charger is working ok.

[bilmet01]

Just saw the following from a post by BehindBars from earlier this year. I did record the voltage of my MBS chassis battery before I started my engine and it read 12.2V. So maybe my BIM is working properly but house charging is not kicking in because my chassis battery is not up to 13.3 yet?



Do a search on BIM logic. TwoPro did some research and a good write up. Here is an excerpt from a thread:

“Here is the logic on the BIM 160.

for MH engine to charge coach:
12v on IGN terminal.
Chassis battery must be above 13.3v.
Coach battery must be below 12.6v.
There is about a 20 second delay
After 1 hour the BIM stops the charging and goes through this same voltage comparison above to see if further charging is necessary.

For Coach Charger to charge chassis battery:
Chassis battery must be above 13.3v
Coach battery must be below 12.6v.
After 1 hour the BIM stops the charging and goes through this same voltage comparison above to see if further charging is necessary.”