Question Max charge on Lithium batteries...80 or 100%?

[Neal]

It seems Apple determined that iPhones, etc. are better max charged to 80% instead of 100%, or something along that line. I think Lithium's in phones may be Lithium Ion vs. what we use which is LiFePO4 (Lithium Iron Phosphate). I wonder if/when we will have controls such as by Victron to set a max charge capacity, assuming we don't, maybe we already do, but controlling the max charge to 80% instead of 100%? Granted we typically think on the lines of we want to be fully charged for usage but for those sitting weeks or months on end on shore power should batteries be capped at 80%?

 

[Kevin D Pem]

Because the BMS in most liFePo4 batteries have passive equalizing circuits, full charge is optimal. 100%

The BMS does the work, if you need to mind the charge, the BMS is not doing it's work.

Set the controller to the specified charge voltage and forget about it.

 

[Richpatty]

I put my RV away (home) and it is usually pretty close to fully charged...but mine is covered (so solar is not functioning) and I don't plug it in. So over time, the small parasitic draws do pull it down. But I can usually get at least a month or so before it gets below 30% or so. And then it is time to take it for its monthly ride where is gets charged back up.

I know what Neal is looking for, and I tend to agree, but for all of the talk about not leaving Lithium's at 100%, there does not seem to be many tools to manage it.

Neal - What does the place you got your systems installed say about this?

 

[Neal]

What does the place you got your systems installed say about this?

I need to ask SES one of these days. I'll email them and pose the question. Need to google a little first too to see if this has been asked in the Victron community.

 

[Neal]

Click here for my google search. Interesting info.

 

[MemoriesByTheMile]

Unfortunately (or maybe fortunately for technical reasons ?) charging systems in RVs are not configured to work based SOC but based on voltage. And even then, voltage seems to be the start of charge trigger and no end of charge voltage trigger.

Turn it on when reaching a certain lower threshold and then run charger for a certain amount of time.

With a table in one hand I can get the charge to start based on a voltage which can be roughly correlated to a SOC. Then I make some WAGs for how long the charge needs to run.

Normally I like to have shore charging stop around 90%ish. When driving it will eventually go to 100%.

I change up the charging profile every couple months to allow the battery to drop down to lower SOC.

 

[MemoriesByTheMile]

Forgot to mention - our LiFePo4 batteries are now around 6 years old and the RV has been used roughly 70% of that time.
Shunt shows what I think is a roughly 6% loss of use, the delta between “Fuel level” and SOC.
Pretty happy with only 6% loss over 6 years of use.

 

[Neal]

In one of the articles I just read in my search for the 80% option there was mention in why Victron wants us to cycle the batteries often, they said in that article twice a month I believe, I do mine monthly per SES is to keep cells balanced and SOC aligned. Makes more sense, so LiFePO4 users probably aren't cycling down low enough and often enough is my guess.