Sunday, November 27, 2022

Another Potential Issue

Friday - An observation that I made yesterday evening after getting an alert from the Victron battery monitor yesterday morning. The alert was for battery voltage dropping below 12VDC on the morning of Nov 24. 

This chart indicates that 12VDC is around 50% charge which is about as low as you want to go when using lead acid batteries. At this point, we had only used about 120AH of the 420AH of capacity. This is the capacity when the batteries were still new. 

I adjusted the battery capacity on the battery monitor to only 210AH, turned off the charging function on the inverter, and we’ll keep an eye on it. The batteries are still working and we do have a generator so it’s not anything critical. Especially since we don’t dry camp a lot.

In the middle of the afternoon, I’m trying to figure out what is drawing 228watts. The refrigerator plus fans are drawing about 80-100watts. The inverter is off and the basement fridge is on shore power. Maybe the two fans are drawing about 80 watts between the pair. All more than I thought. 

 - Early this morning, I checked the SOC (state of charge) and the battery voltage and adjusted the battery bank capacity to match what I was seeing. The battery voltage was still around 12.25VDC so I raised the capacity to 265AH. This raised the SOC to 62% which matches the chart shown above.

I think that our batteries were discharged to almost zero when it was in the shop. Initially, I had the batteries disconnected but the shop needed them on to operate the slides and steps. They were left on for weeks while waiting for parts and when I picked the RV up, the coach batteries were almost completely dead. We may be replacing batteries next month as we won't be able to make it through the night if we need to use the furnace.

A morning project was making this little steering wheel table from wood left over from other projects. The steering wheel is tilted up right now. Some people like driving it the RV with the wheel almost horizontal as it gives them more leverage. I prefer it down at a more familiar angle. 

Sunday - It’s looking like we will be ordering some batteries in the near future. Even without using the propane furnace, our batteries are already dipping down to 60%. 

I’m pretty convinced to get two of the 206AH, 12V SOK batteries without the internal heaters and BT. They are slightly larger and a couple of inches taller than the each of the four existing 6V golf cart batteries. They have a maximum continuous discharge rate of 100amps each so if we upgrade to a 3K inverter, we will need to add a 3rd battery. I am planning to install them in a homemade insulated box in the battery compartment. I can make my own silicone heat pad temperature control with a small WiFi enabled microprocessor. 

I need to also order a DC-DC charger for engine charging. The existing cables are adequate but I’ll need some jumper cables to allow me to remove the existing batteries from the compartment and still have the coach powered up. 

The old Magnum inverter/charger doesn’t have a LiFePO4 charge profile but the solar charge controller does. The Magnum can charge the batteries to ~80% SOC and the solar can top them off if needed. I had originally thought that I needed to change out the inverter/charger first but this should work fine. 


  1. So, the drain on the batteries while in the shop damaged them...

    1. I believe so. They were doing fine last Spring and they were drained down to almost zero several times while in the shop.