question

conradzik avatar image
conradzik asked

Batteries sat unused for years, having issues.

Hi everyone!

For a multitude of reasons, I have a couple of Victron LiFEPO4 12.8v 90Ah batteries that sat completely unused for a few years. Since the day I received them they were never connected to anything. No load or charge.

A few days ago I threw them into my system, one at a time, to charge and try to revive them. I've got a MultiPlus, CCGX, BMV-702 and VE.Bus BMS.

I noticed that my BMV-702 and CCGX's voltage fluctuates between 6V and 10.3V and different states of charge that slowly drops when it switches voltage. At no point do they read a higher voltage. My BMV-702 is set to 90Ah and 13.2V.

I charged both batteries overnight and they seem to be holding a charge. After 24 hours with no load they hover around 13.4V on the meter.

What's the deal with the CCGX and BMV-702 displaying incorrect voltage? Are the batteries shot despite what my meter's telling me?

THANK YOU!!!!

Conrad

Lithium Battery
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2 Answers
Trina avatar image
Trina answered ·

I am not familiar with your particular LifePo4's but the BMS will cut out or shut off to protect the batteries in most situations (esp. with factory AIO drop in types).

So depending on how you have things wired you could see some strange behavior if your reference is not with similar lifepo4's.

I'd say as the BMS was getting things back to balance you were seeing odd things BUT the deciding factor is if they are

(a) Holding and accepting recharging

(b) Able to still serve and deliver capacity as needed

Lithium can sit for ages and does better at mid-charged states for long term storage that would totally destroy all other types of common batteries.

I am guessing once you cycle them a few times they will be fine as long as long as they were decently stored. What you are describing should not have significantly damaged a lifepo4 drop-in AIO unit IMHO

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conradzik avatar image conradzik commented ·

Thank you! I'm trying this. Charging/loading the battery multiple times to see what happens. I seem to be getting decent results, but right now the battery is running down to 11.7ish V and I'm assuming the BMS is killing the inverter. Does that should decent?

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conradzik answered ·

I'm starting to think it's an issue with the BMV-702. BMV-702 disconnected and just the VE.Bus BMS connected through the Multiplus to the CCGX and the CCGX reads the correct voltage. I'm also able to run a 1500 watt load (space heater) for 22 minutes until what I'm assuming is the BMS killing the Multiplus at 46?% and 11.7v. Should a Victron LiFePO4 12.8V 90Ah run longer, or lower? Reading the specs for this battery, around 11.2v should be the load cutoff.

Either way I'm pretty happy I'm able to run a load like that for 22 minutes. Not bad for a neglected battery.

Thanks again!!

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Alexandra avatar image Alexandra ♦ commented ·

@conradzik

We had an issue similar to this, not a victron battery. We had to hold the batteries at full voltage for almost 2 weeks before they were "restored".

The system had a passive balancing setup and a 'weak' cell. All good now though. We just make sure at least once a month it is held at the full charge to keep the battery health up. The bank will switch off or register flat if once cell is not quite up as high as the others as it will discharge first. And need to be protected.

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hendrik-jan avatar image hendrik-jan commented ·

The battery may not be completely balanced yet. To get the max Ah the cells need to be top balanced. Top balancing for the bluetooth batt works best at 14.2V with a BMS to stop the charger when 1 cell get into overvoltage.

With the info from you about your test, I calculate roughly the Ah: load 1500W multi eff 80% average Vbat 12V (under 2C load), Ibat would be: 1500W/(0.8*12)=156A. The Ah you probably have drawn was : 156A*22min/60min = 57Ah.

That the system stopped at 11.7V with more than 1C of load is normal, because 3V per cell (no load) is considered empty and the shutdown value is 2.8V cell voltage.

My guess is that if you charge it to 14V and do the dis-charge test again, the battery last longer with your 1500W load and probably measures 90Ah.

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Alexandra avatar image Alexandra ♦ hendrik-jan commented ·

@Hendrik Jan

Yes the balancing is the key to a healthy bank and being able to use the capacity too.

Sounds like you are making progress in the "therapy" sessions though with your batteries.

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