Forum Discussion

Janss's avatar
Janss
Explorer II
Jan 11, 2014

Battery disconnect switch

We have two 12v house batteries dated 02/11. Best I can tell from my very limited knowledge, they are wired in parallel (+ to +, - to -).

We are currently hooked up in an RV park for the winter. I believe one of the batteries is bad. When I checked, water was empty in most cells, and when I filled it, water sounded and looked like it was boiling inside. Also the sulfur smell. The water level in the other battery was fine when checked...didn't need to add any.

So question is what do I do until I can get two new batteries installed (which I won't be doing myself). There is a battery disconnect switch. Motorhome book says to always leave it on except for long periods of storage. Converter book says that the converter does not need the batteries connected to operate properly.

Since we are plugged in to electric, what would be the effect of pushing the battery disconnect switch? I actually tried it already. Does it disconnect the batteries from the converter or the batteries from the 12v appliances (e.g. lights)? Because I checked the voltage on the power management panel and it still shows the same as before (13.6). Also I thought the lights wouldn't work, but they still do.

Please help.
Class A
  • Passin_Thru's avatar
    Passin_Thru
    Explorer
    Jan 12, 2014
    It cut's off 12 volt feed into the MH when disconnected (or connected) to outside power. Yes you can push the disconnect button. Being hooked to electric, you have a charger built in to your inverter which keeps the storage batteries charged. You may use a 1/2 inch wrench to loosen the cable bolts, wearing gloves is a good idea and just disconnect the alleged bad battery, take it to nearest auto parts battery store Costco etc and exchange it for a new one. Stop at the auto store for some batter terminal lube and a battery terminal brush, clean the inside of the cable of all dirt, go put it back together being careful not to break the terminal off when you tighten the cable. http://carbatteryonline.net/how-to-change-a-car-battery.html
  • pianotuna's avatar
    pianotuna
    Nomad III
    Jan 12, 2014
    Hi Janss,

    The battery disconnect switch disconnects the entire battery bank from the "house" part of your RV.

    Here is more detail on what to do:

    1. turn the disconnect switch *off*
    2. disconnect the negative cable from the suspect battery
    3. disconnect the positive cable from the suspect battery AND cover the connector with insulating electricians tape or similar.
    4. turn the disconnect switch back *on*
    5. enjoy your holiday
  • Janss's avatar
    Janss
    Explorer II
    Jan 12, 2014
    Okay, thanks for all that. If we didn't actually disconnect cables, what does the battery disconnect switch actually do? (See my initial question.) And how does being hooked up to electric affect that? And is it okay just to press the disconnect button while being plugged in?
  • garry1p's avatar
    garry1p
    Explorer
    Jan 11, 2014
    You are correct the batteries are in parallel.

    You can remove the suspect battery and take it to any auto parts store for testing. It would be best to replace both batteries at the same time.

    You have the option of just using the disconnect switch but a bad battery will take out the good battery given time.

    You can remove the cables from the bad battery completely or just disconnect the cables from the bad battery.

    Be careful with the cables if you just disconnect and leave the cables attached to the good battery as the + cable will be hot. Once disconnected wrap a rag or plastic bag over the end of the removed hot (+) cable so it will not contact anything. It will not shock you but will create a big spark if it hits any metal.
  • jwmII's avatar
    jwmII
    Explorer
    Jan 11, 2014
    The way I read it ,He is telling you to remove the negative cable from the supposedly bad battery. Then remove the positive cable that goes to the supposedly bad battery from the good battery,thus taking the bad battery out of the loop.After reaching that point I would go one step farther and remove the positive cable from the bad battery. Then test the bad battery. Sopposing the battery is bad and needs to be replaced will present you with the question of replacing both batteries. You really should not parallel a new and old battery since in parallel they feed off each other and the weaker or older will bring the new battery to its level denying you the full benefit of a new fully charged battery. The long and short of it, is to replace both batteries for the best battery life.
  • Janss's avatar
    Janss
    Explorer II
    Jan 11, 2014
    What do you mean by this:
    "Do this at the good battery leaving the good battery connected."

    Do you mean remove the negative cable off the bad battery, then remove the positive cable off the bad battery....leaving those two cables still connected on the good battery?

    I am not a DIYer but may be able to at least disconnect the cables.
  • donn0128's avatar
    donn0128
    Explorer II
    Jan 11, 2014
    All you have to do is first remove the negative cable from the bad battery, then remove the positive cable. Do this at the good battery leaving the good battery connected. This will isolate the bad battery and allow you to remove it for testing. Very easy project for a DIYer.

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