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Did I Kill My Battery?

TinnitusTinnitus Member Posts: 26
in Battery/Electrical & Solar
I have a 2020 T@B 400. It's been in storage for about 6 months. Getting ready for a long trip a few days ago, I noticed that the power inverter by the door was buzzing. It had somehow inadvertently been left on, the light on the panel shining, since our last camping trip. (The battery switch in the back storage area was OFF the whole time!)

I turned off the inverter, turned the battery switch on and checked battery strength on the T@B display by the door, which said "low" battery, even though there is a solar panel on top, and the interior display for that was showing that it was charging: battery status "low". I checked back the next two days, the inverter off, the solar panel still charging and the battery status was still "low". 

Today, I drove for 550 miles (connected to the truck, of course) and the battery status is still reading "low". The inverter was off the entire trip. 

I was very much hoping that the long drive would have charged the battery back to full again. But nope, according to the T@B panel by the door. The interior display for the solar panel agreed: "low" battery. 

So what have I done?

And why was the inverter even powered, when the battery switch in the storage area was "off"?
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    VictoriaPVictoriaP Member Posts: 1,494
    Most modern vehicles have “smart” alternators and don’t do much to charge RV batteries unless you have a DC to DC charger installed. Your best bet to charge is to plug the trailer in via the 30 amp cable for at least a full day. 
    2019 320s BD Lite, white with blue (“Haven”)
    2015 Subaru Outback 3.6r (unsafe 200lb tongue weight limit until 2020 models)
    2020 Subaru Outback XT
    Pacific NW
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    pthomas745pthomas745 Moderator Posts: 3,705
    edited June 2023
    The panel near the door is...not good enough for battery monitoring or solar power status.  What it might see as low..an actual voltage readout might be very low on your battery.
    Do you have the Victron App?  Or a multimeter?  Or anything that might show you the actual status of the battery?  If the inverter has taken the battery down repeatedly, and the solar panel has not been able to keep up..this might be the issue.  The inverter running uses over an amp and a half per hour, so that is a big ask for a solar panel to handle on an everyday basis.
    Having said that: the battery switch question is a bit of a conundrum. 
    But, get the Victron app. Or a specific multimeter so you can get an actual rested battery status.  When you can get a more reliable voltage reading, then you can work some more troubleshooting steps.
    2017 Outback
    Towed by 2014 Touareg TDi
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    MarcelineMarceline Member Posts: 1,513
    pthomas745 said:

    Having said that: the battery switch question is a bit of a conundrum. 
    But, get the Victron app. Or a specific multimeter so you can get an actual rested battery status.  When you can get a more reliable voltage reading, then you can work some more troubleshooting steps.
    I seem to remember someone else saying that the T@B400 inverter is wired straight to the battery (so it is not on the switch). 
    San Francisco Bay Area
    2013 CS-S us@gi
    Battered but trusty 3.5l V6 Hyundai Santa Fe
    2015 Toyota Tacoma PreRunner Double Cab
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    Grumpy_GGrumpy_G Member Posts: 466
    Inverters can draw a lot of current and thus are typically directly wired to the battery. Maybe somebody with a similar vintage 400 can confirm this. 

    With the battery switch on and driving for 500+ miles plus solar you should have gotten some charge back. There is a good chance the battery is indeed dead. What likely happened is the inverter slowly drained the battery and during the day solar only got a small charge into the battery. So the next night the battery got drained to almost nothing again. That kills a battery quickly. 

    The "smart alternators don't charge RV batteries" claim is bogus. If you parallel an almost dead battery with the vehicle battery it pulls down the voltage enough that the alternator increases its output. Even if the smart alternator is in its happy place it will still output around 12.5V, enough to breathe some life into a discharged battery. 

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    ColMagColMag Member Posts: 16
    Unfortunately, I would guess the battery is done-for. The inverter and solar charge controller do not go through the main battery shut off switch, so are the only things wired directly to the battery. And the inverter just on standby uses a lot more power than the charge controller. Even the solar charge controller uses enough power to really run down the battery (if solar panels covered) if the battery doesn't go into winter storage first fully charged---our 2022 TAB 400  went in full and came out depleted by about 1/3... Next time I'll also change the charge controller's Setting to OFF and/or pull its fuse first.
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    pthomas745pthomas745 Moderator Posts: 3,705
    @Marceline @Grumpy_G @colmag thanks for the reminder of how the inverter is actually wired.  Now I remember all those posts from the first few models of the 400 where the inverter being left on drained batteries.
    2017 Outback
    Towed by 2014 Touareg TDi
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    BinghiBinghi Member Posts: 280
    FWIW, here is the battery compartment in our 2021 400 BD. I have the original 6V Harris AGM’s. I believe that blue device is the inverter. Its cables head toward the passenger-side outdoor storage compartment. I wonder if they connect to the circuit breaker complex located on the inner wall of the outdoor compartment.


    2021 400 BD / 2016 VW Touareg / Austin, TX
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    HoriganHorigan Member Posts: 622
    Given the high currents going to inverters, they are typically wired directly to the battery or battery junction box/bus bar with very thick wires.  Typically much thicker than the wires running through the battery disconnect switch.  I suspect there is a distribution block or bus bar just left of the picture above.
    Rich
    2019 T@b 400
    2013 Toyota Highlander 3.5L V6
    Bellingham WA
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    TinnitusTinnitus Member Posts: 26
    Thanks everybody for the info. I am certain that the sales guy at the RV dealership did not tells me about the inverter being wired directly to the battery, and it never occurred to me to ask. As I said, leaving it on was an accident. I'm normally attentive to turning that off when leaving a campground. 
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