House battery drain

[Cherguin]

I have a 2018 Coachman Mirada kb35.  I parked it the day after Christmas (6 days ago), shut everything down and turned the house battery switch off.  This morning I go out and the house batteries are tanked at 10.1 volts.  They are 1 year old Duracell 6 volt batteries in series.  This has never happened before.  What could possibly drain the house batteries with the master switch off?  What is still “connected “ to the house batteries with the master switch off? 

[opnspaces · Accepted solution]

Two things come to mind.

1. You have a damaged or dead battery. Battery cells are about 2.1 volt each when fully charged. Your 6 volt batteries each have 3 cells at 2.1 volts. Put two 6 volt batteries together and you have a total of 6 cells (3 cells per battery) x2.1 = 12.6 volts. If you have a single dead cell you will lose 2.1 volts and see 10.5.
2. It's also possible that your battery disconnect does not completely disconnect all loads from the battery. It's common for manufacturers to leave certain loads separate from the main loads that go through the switch. These parasitic loads can drain a battery in a week or two.

First take a few pictures of the wires as they are connected to the batteries. Then temporarily disconnect the wire in the middle that joins the two batteries together and take a voltage reading from each battery. Write this number down. Then hook the batteries back together and charge them up fully.

After charging fully, disconnect the wire in the middle again. Disconnecting this middle wire will both isolate the batteries from each other and isolate them from the coach. Now periodically take voltage readings over the next week and see if any of the batteries are losing significant Voltage.

If a battery loses voltage down to 4.2 (meaning you lost one cell at 2.1 volts) you need to replace that battery.

If after a week disconnected your batteries are still fully charged it's time to hook the middle wire back up. Make sure the battery disconnect is set to disconnect the batteries from the RV. Take a voltage reading from the two battery terminals that are hooked to the wires headed into the RV. You should have somewhere around 12.6 volts. Write it down and then check the voltage daily for a week. If the voltage starts dropping your disconnect is not a complete disconnect.

[crollman · Accepted solution]

I'll second the words about parasitic loads that remain active when the main switch is off.  I added a cutoff switch right at battery in order to prevent this from happening.

[Vintage465]

Did you find out what the drain is?

[Gjac · Accepted solution]

I would disconnect the negative cable and set your multimeter to amps connect the two leads between the post and neg cable end and see what your parasitic draw is. If it is several amps or more, you have something on like a light in a storage bay. If less than an amp or so, check your battery it may have a shorted cell or be on its way out. Being that the batteries are a year old, and you already disconnected the neg terminal, when you return from your trip after 6 days take another reading, if they are still fully charged you know something was left on. If you still read 10 volts you know your battery is bad assuming that you fully charged your batteries both times.  

[Cherguin]

Thank you very much.  I’ll be back in town next week and give it a try.  

[Vintage465]

The first thing to do is see if you accidently pulled the brake-break-away cable.  Nothing is easier to do than that and nothing kills a battery bank faster than that.   Two times I flattened my battery bank and once was cause of the break-away cable and the other was becuase I left a light on in the pass thru.

[Cherguin]

The MH was in storage so no breakaway cable attached.  

[Cherguin]

Thank you VERY MUCH for a thoughtful and detailed response, on New Year’s Eve no less. What you suggest makes perfect sense and I will do as you described when I get home Tuesday.  For now I have disconnected the negative terminal so I don’t get any further drain from parasitic loads if that is the issue. 

Happy New Year!

Sherwood

[opnspaces · Accepted solution]

Two things come to mind.

1. You have a damaged or dead battery. Battery cells are about 2.1 volt each when fully charged. Your 6 volt batteries each have 3 cells at 2.1 volts. Put two 6 volt batteries together and you have a total of 6 cells (3 cells per battery) x2.1 = 12.6 volts. If you have a single dead cell you will lose 2.1 volts and see 10.5.
2. It's also possible that your battery disconnect does not completely disconnect all loads from the battery. It's common for manufacturers to leave certain loads separate from the main loads that go through the switch. These parasitic loads can drain a battery in a week or two.

First take a few pictures of the wires as they are connected to the batteries. Then temporarily disconnect the wire in the middle that joins the two batteries together and take a voltage reading from each battery. Write this number down. Then hook the batteries back together and charge them up fully.

After charging fully, disconnect the wire in the middle again. Disconnecting this middle wire will both isolate the batteries from each other and isolate them from the coach. Now periodically take voltage readings over the next week and see if any of the batteries are losing significant Voltage.

If a battery loses voltage down to 4.2 (meaning you lost one cell at 2.1 volts) you need to replace that battery.

If after a week disconnected your batteries are still fully charged it's time to hook the middle wire back up. Make sure the battery disconnect is set to disconnect the batteries from the RV. Take a voltage reading from the two battery terminals that are hooked to the wires headed into the RV. You should have somewhere around 12.6 volts. Write it down and then check the voltage daily for a week. If the voltage starts dropping your disconnect is not a complete disconnect.

[crollman · Accepted solution]

I'll second the words about parasitic loads that remain active when the main switch is off.  I added a cutoff switch right at battery in order to prevent this from happening.