Limiting SoC for longevity?

Anyone have a good method to limiting SoC? I've oversized my system by about 20%, and was thinking of invest that oversizing towards longevity, by not charging to 100% each time. This is on an RV/van, I have all three methods of charging, solar, alternator, and shore/generator. I'm planning on four drop-in 12v batteries in parallel, and each has it's own BMS that does not allow customization.

My thought was to use a single Victron Smart Battery Protect that takes all the positive cables from the chargers to the battery, and set overvoltage to ~13.2v. This way it will disconnect the charger(s) once it reaches about -85-90%, but not keep floating up to 13.6v. I'd also have a relay to bypass the protector in case I did want to bring it up to 100%.


I have no experience w/ the Victron Smart Battery Protect, so I'm just spitballing here. Any other thoughts are welcome.

Lead Acid or LiFePO4?

This is for LiFePO4.

I also found this on my trip down this rabbithole, which seems like I can just set a cutoff voltage, and a restart voltage, which means I can just use the non-smart battery protect that's half the price (or even just a standard switched isolator).


Instructions are in a PDF:

DIYVan said:

I have no experience w/ the Victron Smart Battery Protect, so I'm just spitballing here. Any other thoughts are welcome.

Click to expand...

I think you might be over-thinking this. A good quality LiFePO4 battery is usually rated for around 3,000 cycles, at one cycle per day that's just over eight years, and even then you still have 80% capacity! Have you seen the SoC versus cycle life for LiFePO4? You maybe get a hundred or so more cycles if you limit DoD to 80%. I just wouldn't bother. In two years time when super-magneto-flux-ribbon battery technology is mainstream, you'll be replacing your 'outdated' LiFePO4s. Charge to full, discharge to empty, wash-rinse-repeat. Life is too short (and technology development too fast) to worry about LiFePO4 longevity.

Just my opinion ... other opinions are available!

I believe the stated 3,000 charge cycles is at optimal conditions, the reality is I'm unable to control the temperature to a great degree, since I don't have enough solar capacity to actively cool the storage area at all times. I can control the storage SoC though.

@Will Prowse made a video about this.



I guess my concern is that they would be stored in prolonged elevated temperatures in the summer. If you compound these effects w/ deep cycling the batteries, I have a potential to lose much more in a shorter period of time.

The referenced material:

Reference the Noyito voltage module... has anyone tried this?
I landed at the same strategy.. the module driving a high current relay with a bypass switch to restore full capacity When required.
In my case, managing a dual battery setup in the back of a truck, I am combatting high temperatures and an under-used Lithium battery that will sit at 100% for 99.9% of its life if I don’t do something. The jury is in... this is a bad idea!