coltarkdm avatar image
coltarkdm asked

What settings are needed to keep my 4 Battle Born batteries from charging past 90%?

Maybe I'm going brain dead, but I have four battleborn batteries which is more than sufficient for me. Because of that, I want to maximize my battery life by ensuring that they never charge past 90% - 95% state of charge. What settings do I use to make that happen? TIA!

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Alexandra avatar image Alexandra ♦ commented ·

@ColtarKDM Check the manual for this under the section storage and maintenance, but it does recommend charging the batteries to 100% at least once a year.

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coltarkdm avatar image coltarkdm Alexandra ♦ commented ·

Thank you Alexandra!

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2 Answers
wkirby avatar image
wkirby answered ·

To prolong the life of the cells, the key is Voltage rather than a specific percentage.
So, if you consult the battery documentation, the acceptabe Voltage range for the Absorb stage is 14.4V to 14.6V for a 12V Battleborn battery.
So, set the Absorb stage to 14.4V. You could aslo lower the Float Voltage if you like.

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coltarkdm avatar image coltarkdm commented ·

Thank you WKirby1

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ttbb avatar image ttbb commented ·

@WKirby . Can I ask what studies/evidence this is based on?

" SOC represents the proportion of ions present on either electrode, thus, for high SOC there is a significant number of lithium-ions available at the graphite electrode to partake in potential side reactions with the electrolyte."

With NMC you can't get to the higher states of charge without the higher voltage. The logic there is very simple. Higher voltage = higher state of charge, lower voltage = lower state of charge.

In respect to lithium-ion phosphate, I have personally not read anything that clearly indicates lower voltage is the 'key' to reducing degradation that negates the effects of hight states of charge. The one thing it clearly does do is naturally regulate the current entering the cells for the last bit of the charge. A tapering constant voltage charge hit at a lower voltage / earlier in the charge. That, in turn, can reduce heat build-up due to the higher internal resistance at high states of charge. That is all relative to your initial charging current and size of the pack though.

"But the damage to the battery is not only due to high voltage. It is due to more complex reactions of which voltage is but only one parameter."

So In the pursuit of knowledge, I would be interested in any studies you can reference that indicates the drop in charge voltage is the key to longevity in a lithium-ion phosphate.

From another perspective, charging at 14.4v over 14.6v might be more beneficial for cell balancing offering a longer period at a fixed constant voltage when the BMS systems can balance out cells.

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wkirby avatar image wkirby ♦♦ ttbb commented ·
It is down to the dielectric strength of the separator material. The separator needs to be as thin as possible to enable high energy density. However it also needs to be able to electronically separate the anode and cathode. If the Voltage differential is too high then electrons will be able to penetrate the separator and damage it. Although the separator is made to high tolerances, there are still tolerances and cells cherged right to the margin may have small areas that are slightly thinner and may allow penetration. So keeping the Voltage lower helps to mitigate these manufacturing tolerances and help to prolong the life of the separator. Capacitors also have Voltage limits, and designing circuits well within these limits or selecting capacitors with Voltage limits with lots of headroom prolong the life of such devices. This is how it was explained to me at the Victron training that I attended. If I have time, I'll see if I can dig up any references to what I have explained. I hope that helps a bit.
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mmsi2022 avatar image
mmsi2022 answered ·

This is a great conversation and I'm glad I found it before posting a question about this. I have a 7.5kWh battery in my boat made from 21 Nissan Leaf modules, and I have two different battery profiles configured, one charges to and then floats at 54VDC, which is approximately 40% SOC, and another profile that charges to 58.8 to take it to 100%.

Any thoughts on an easy mechanism to swap between these battery profiles? Right now using VRM to access Cerbo GX to load a new config to the Multiplus 48/2000 on VE.BUS.

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