Need Chassis Battery Advice on 2 yo MH

[flyboy013]

I need some advice on diagnosing a chassis battery problem on my 2018 Newmar/Spartan K3.

About a year ago I started noticing that when dry camping my chassis battery voltage would be low (12.3 or less) come morning time. And this problem has continued and I’m not sure if the problem is a parasitic draw or bad batteries, or perhaps something else.

A few months ago I had connected an ammeter inline on the negative side of the battery and found that I had a draw of 350-400 mA. I isolated a majority of the parasitic draw to the Spartan Control Module (SCM) which Spartan then replaced. More recently, I’ve measured the draw at about 130 mA which seems slightly high, but acceptable. My online reading has indicted that for a car 50 mA is around normal. So 130 mA isn’t doesn’t seem all that high especially given that I have two 930 CCA wet cell batteries. When the SCM was replaced the shop also did a load test and I was told that the batteries were okay. Here’s a picture showing what batteries (2) I have.



I’ve been adding a smart home capability to the MH and have been capturing data on the battery voltage and when the bidirectional isolator relay is engaged. Here is a graph for the last 48 hours.



You’ll notice that the bidirectional relay will kick on about every 3-4 hours and stay engaged for 1 hour (maximum configurable time). Given that I’ve let my car sit for 3 months and still have a reasonable voltage, I expect the chassis batteries to only drop below 12.5 and have the need for the bidirectional relay to engage after at several weeks or more, not every few hours.



I drove the MH to the a dump station yesterday. It was a 30 minute drive with the batteries charging (via alternator) along the way. When I got out of the vehicle to dump, I forgot to turn my headlights off and after 3-4 minutes the generator started due to the low chassis battery voltage. I was a bit surprised by this and this makes me think the problem I’m having may be with the batteries as opposed to a parasitic draw.




I pulled the batteries out of the vehicle and checked the water level, all was good although I did top them off slightly.

So, what do these symptoms point to? Is there additional testing I can perform myself (ie a specific gravity test with a hydrometer)? Should I take the batteries somewhere for more testing? If the batteries are bad, wouldn’t the load test that was previously performed have shown the problem? Looking for guidance on how to proceed.

Thanks!

[Gary RVRoamer]

I think you will find that there are things powered from the chassis batteries in a coach that don't exist in a car, e.g. the powered entry steps, LP detector, etc. Slide out motors too, which means there is some stand-by power draw in that controller as well. Modern electronic devices are never Off unless disconnected - they have active circuit boards waiting for input, e.g. someone pushing the On button.



IMO, 130 ma is about as low as it is likely to get.

[flyboy013]

Originally Posted by Gary RVRoamer

IMO, 130 ma is about as low as it is likely to get.

Thanks. Now I just need to determine how best to test the batteries to ensure they are bad before I spend ~$800 for two new upgraded AGM batteries.

[Milford 47]

load testing is by far the best way

[flyboy013]

After further analysis, I determined that the 2 year old Harris batteries were bad. Yesterday I replaced them with two NorthStar Group 31 AGM batteries. I’ve been monitoring the battery voltage for the last 24 hours and it hasn’t dropped below 12.8 volts (as opposed to the old batteries dropping from 12.8 to 12.4 within two hours).

When I had the Spartan Control Module replaced in September, the service center had tested the batteries and they were supposedly good. But given the symptoms such as the voltage dropping well below 10 volts when starting the engine and the battery dropping to 12.4 volts within three minutes of turning the coach off and leaving the headlights on, I figured the problem was the batteries as opposed to a parasitic draw draining the batteries.

I’m not quite sure why the batteries failed. It seems like there’s quite a few posts blaming dealers for not properly maintaining the batteries when parked on the lot, but this coach was picked up at the factory shortly after it was built. The coach is plugged or being driven nearly 100% of the time, so the possibility of having the batteries drained below an acceptable level is very low. Perhaps the batteries were just bad from the start.

As for the parasitic drain that I measured, my readings were not accurate. It appears that when I disconnected the battery ground wires to put the ammeter inline, Silverleaf detected a low chassis battery and engage the bidirectional isolator and thus chassis components were pulling power from both the chassis and house batteries resulting in an low reading from the chassis battery.

I found that 590 mA was being drawn by the front PDC. Of that 270 mA was being drawn by the Newmar installed KIB accessory board, 256 mA by the Spartan Control Module and/or Hadley system, and 50 mA via the drivers seat fuse. I disconnected the three connectors that I found on the drivers seat but was unable to isolate the 50 mA. Of the 270 mA being drawn by the KIB board, 115 mA was being drawn from the Xite navigation system (which was powered off). I isolated a few other items, but nothing significant.