That's not a concern, is it? We're talking about battery backup, meaning the "expected use case" is that the Lead-Acid battery is sitting at near 100% capacity for almost its entire life, without significant amounts of discharge. Sure, you've got to discharge when the sun goes down but I don't expect a properly-sized battery to be deeply discharged (especially when we're aiming for multiple days worth of "worst-case" power, like multiple days of clouds/rain to reduce our power-collection).
Lets just be dumb with napkin math for a second: 12-hours of charge, 12-hours of discharge on a "typical" day, with a 3-day / 72-hour period of worst-case charge. Where does this leave us?
12-hours of typical discharge / 72-hours of worst-case discharge == DoD of 100% to 83% on your typical day-to-day basis.
Hardly anything that considers a "deep discharge". And if we really need deep-discharges, most Lead-Acids can survive something on the order of 300x to 500x deep discharges right? So its not like the 5 to 10 times a year where you need all 72-hours of battery are significantly hampering your lifespan?
> And even then is longevity of lifepo4 so much better it’s not funny.
Measured in deep cycle-counts (ie: cell phones or laptop usage), sure. (like 3000 cycles on LiFePo4 vs 500 on Lead Acid). But years of sitting on a float-charge, I don't think its that much better than Lead-Acid.
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That being said, LiFePo4 is a "superior" battery for sure, and its much cheaper than I remember. But Lead Acid remains significantly lower-priced than LiFePo4 as far as I can tell (2-to-1 or less)
I think you have a point about Lead-Acid charging slower when its near full (and keeping it full is key to keeping Lead-Acid long-lasting). So I admit to not recognizing that (LiFePo4 also charges slower when near full, its just that it charges like 3x to 4x faster than Lead Acid so its less of a concern)
> Please spend the extra money on lifepo4, save yourself some headaches.
We're at the hobbyist level where the original post decided that MPPT solar charge controllers weren't needed (at least, in an earlier version of this project)
Clearly no one here is talking about the strictly most optimal design, but are instead talking about simpler and cheaper solutions.
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Simplicity here is key. LiFePo4 does _NOT_ like topping charges or staying at 100% charge for long periods of time. Lead Acid however, prefers 100% charge and UPS use Lead Acids for this reason.
LiFePo4, in UPS/Standby like systems, need to stop charging, and wait for the battery to be used before engaging in a new charge cycle.
Lead-Acid on the other hand, can just have a constant voltage applied (ex: 13.5V or so) and you can just hold that indefinitely, for incredibly simple standby circuits.