wulfraat avatar image
wulfraat asked

Charging lithium to 100% SOC

In my Airstream travel trailer I have two 300ah 12v Victron Smart Lithium batteries in parallel, BMV 712, 800w of solar, Victron 150/70 MPPT controller and MultiPlus for shore power / genset power for charging.... and CCGX for system coordination.

I also own a Telsa, and the best practice, generally speaking, is to run the lithium pack between 30% and 70% SOC to maximize longevity. We only ever charge to 100% ever 2-3 months when needed for extended use. It has active cell balancing, of course.

The Victron batteries have passive cell balancing, which of course means you must charge and float at 100% SOC to balance the cells.

My question is - does charging the Victron 12v Lithium batteries to 100%, over and over again (on a daily basis) degrade the performance of the Victron lithium cells at an accelerated rate? Or... should I manage the batteries like I do the Tesla cells - between say 30 and 70% SOC, and only fully charge / balance on, say, a monthly basis?

In other words, what are the best practices for yielding the longest lifespan / longevity from Victron 12v Lithium batteries aside from caring for them with low charge / discharge currents?

Thank you Victron community :)

battery chargingLithium Battery
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3 Answers
mvader (Victron Energy) avatar image
mvader (Victron Energy) answered ·


At 100%, the batteries are not that full yet that you really decrease longevity significantly.

And for the rest its inherent to the design: you’ll have to fully charge the batteries regularly to prevent imbalance between the cells. There is no other way; but besides that I wouldnt worry about this if I were you. Its all a bit on the theoretical side.

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irwinr avatar image
irwinr answered ·

It might be useful to point out that the Victron Lithium cells don't use the same chemistry as Tesla. Not all "Lithium" chemistries are the same. Victron uses "Lithium Iron Phosphate" (Often abbreviated LFP) whereas Tesla uses "Lithium Nickel Cobalt Aluminum Oxide" (Often abbreviated NCA). You can read about the various chemistries here:

LFP is a bit of a stand out in the Lithium battery chemistry crowd. Most of the other chemistries are fairly similar aside from LFP. Battery Univerisity describes LFP like so:

"Li-phosphate offers good electrochemical performance with low resistance. This is made possible with nano-scale phosphate cathode material. The key benefits are high current rating and long cycle life, besides good thermal stability, enhanced safety and tolerance if abused.

Li-phosphate is more tolerant to full charge conditions and is less stressed than other lithium-ion systems if kept at high voltage for a prolonged time. (See BU-808: How to Prolong Lithium-based Batteries). As a trade-off, its lower nominal voltage of 3.2V/cell reduces the specific energy below that of cobalt-blended lithium-ion."

So basically LFP is a lot more expensive than NCA, and doesn't carry as much energy per volume or weight... But LFP is able to tolerate being kept at near 100% charge without as much degradation as chemistries with higher operating voltages. It's still better to not keep it at 100%, but an LFP cell maintained at 100% will likely outlast a Tesla cell kept at 80%. I usually aim to keep my cells at 3.4v/cell rather than the "100%" charge which is 3.6v per cell. With LFP 3.4v per cell drastically increases service life and 3.4v/cell still gives you 95%+ SoC.

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solarhack avatar image solarhack commented ·

How do I configure my Multiplus II / MPPT to not charge to 100%, say 98%?

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irwinr avatar image irwinr solarhack commented ·

See my response to Wolle4000 below.

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wolle4000 avatar image wolle4000 commented ·

It all sounds very plausible. But what values do I have to set in my Victron Quattro to reach the 3.4V discharge voltage? I have Winston cells with an active BMS from REC

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irwinr avatar image irwinr wolle4000 commented ·

If they are 12v batteries that means 4 cells in series. So to charge each cell to approx 3.4 you need to charge the battery to (3.4v per cell) x (4 cells in series) = 13.6

I simply set my absorption and float charge values to 13.6.

You might want to occasionally charge them to 14.4-14.6 (3.6 to 3.65v per cell) to keep them balanced, maybe like once a month or so.

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friaras avatar image
friaras answered ·

With newer cells, the specs might change, check with the manufacturer, on my batteries the data sheet specs are different and I have verified this with the manufacturer.

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