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Old 04-29-2020, 05:31 PM   #1
Happy Fuse Owner
Join Date: Oct 2018
Location: Apache Junction, AZ
Posts: 473
What is going on here?

A couple of days ago I had my AGM batteries replaced with 2 BB Lithium batteries and today I decided to see how they are working. The RV is in storage and I went to it and checked the voltage - 14.2 volts.

The RV still has the old wet cell converter/charger (Progressive Dynamics PD9245C) but I bought the pendant which is supposed to boost the output to 14.4 volts for about 4 hours and then drop back to 13.6. I plugged the RV into a 110 outlet and set the Progressive Dynamics pendant to Boost and left it for about 6 or 7 hours with the fridge (Norcold DC0061 compressor) on.

When I went to check it the battery voltage was down to 13.6 volts (as measured by the Zamp solar controller) but I assumed this was because the input voltage had dropped back to its normal charging voltage of 13.6 volts and I was seeing that. I unplugged the electric and expected to see the voltage jump up to 14.2 or so volts, but instead it remained at 13.6 volts. The fridge is still on since we are getting ready for a local trip and when I checked, 10 minutes later, the voltage was down to 13.3 volts. My Victron battery monitor says the batteries are good for another 1 day and 17 hours, but why is the voltage 13.6 and not 14.2 (or so). Is something wrong? Or is this what is supposed to happen?

Some information - 2018 Winnebago Fuse. 300 watts of solar (which is not of any use right now because the storage is covered, not a bad thing in southern Arizona) and the draw on the batteries was almost 5 amps when I left. It is hot outside and the fridge is working pretty hard. The inside of the RV was 96 when I was there but it would have been considerably hotter had the RV been in the sun.

There is one other thing that bothers me. The Victron battery monitor is set up based on the BB settings for their batteries, in particular the base voltage is set to 14.2 volts. Since the voltage on the solar controller showed 13.3 volts why would the battery monitor say the battery was at 100% of the full voltage is supposed to be 14.2 volts? Or can I not trust the voltage on the solar controller?

Or am I missing an even bigger point here?
2018.5 Winnebago Fuse
AJMike is offline   Reply With Quote
Old 04-29-2020, 07:02 PM   #2
Join Date: Mar 2018
Posts: 492
Against my better judgement ...

Bottom line is lithum batteries are strange animals. Anything around 13.4-13.6 volts on a standard voltage display is probably 100% full or very close. Or not?That's part of the fun of lithium batteries, the "not knowing" your exact SoC.
If I see my Zamp CC tell me that my batteries are FUL, they're usually somewhere near 13.4V - 13.6V. The One Place display is usually close to these numbers, or maybe 1/10 volt lower. Once again, I'm good with "close". I am not a battery/off grid power micromanager. If stuff works on 12V, I'm happy.
2018 (2017 Sprinter Cab Chassis) Navion24V + 2016 JKU (sold @ ????)
2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
2002 Roadtrek C190P (sold @ 315,000kms)
Winterbagoal is offline   Reply With Quote

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