Over the years, I've generally made the observation that those who really slam lead acid for energy storage use seem to have been nowhere near a modern lead aci

Over the years, I've generally made the observation that those who really slam lead acid for energy storage use seem to have been nowhere near a modern lead acid datasheet from the last 20 years, and that seems to be the case here as well. They also tend to make assorted arguments in the context of off-grid power that don't reflect the realities of off-grid power systems in annual use. The mid-range Trojan Solar Premium line (my office runs an older version of this, the T105-RE and I'm five years of daily cycling in with what seem to be entirely healthy batteries still) datasheet [0] shows a 3500 cycle life at 30% DoD, which is 10 years of daily cycling use. However, depending on loads, panels, and how you use the place, you'll typically see far shallower cycles in the spring/summer/fall, and then some deeper cycles in the winter months. So you can average it out - a single 80% discharge isn't going to have a huge impact on longevity, just don't do it all day, every day. If you've got enough panel area to recover a low battery bank in a good day or so of sun (generally recommended for off-grid), you'll have enough panel area to ride through daytime loads most of the year without really bothering the battery pack either. The Solar Industrial line [1] is rated 3500 cycles at 50% DoD daily cycling, and about 6250 at 30% DoD. Good luck finding them, though. They also, as has been discussed elsewhere here, don't need heating in the winter to be able to charge safely. I generally don't like charging lithium below about 45F, and even that would be a low C-rate. Not having to heat lead makes winter an awful lot easier. As far as the rest of your claims... they mostly don't matter for a typical off-grid power system, which is the general context of this thread. Coulombic efficiency for lead varies rather significantly depending on where in the state of charge, and it's not really reasonable to discuss "average" numbers for lead. Once you're full, up in absorb, the CE is quite poor, as it's gassing, but that's also required to mix the electrolyte and prevent stratification, so it's still doing something useful. However, the times when it matters - cold, dark winter months, if you're running partial state of charge cycling (which the modern carbon additives allow without the problems of hard sulfation), the CE during charging is quite good - near 100%, as long as you're below gassing. So when CE matters, when you're power limited, it's perfectly reasonable, and when it doesn't matter, when you have a surplus of power, it's poor. I don't particularly mind that. As far as internal resistance goes, it's certainly far worse than lithium, but at typical off-grid C/20, C/8 type rates, it just doesn't matter that much. Nobody is asking deep cycle off grid lead to deliver starting amps for a tractor, and it won't do it, because it's a substantially different internal design than a starting battery (which have far lower internal resistance - go measure one sometime, it's pretty impressive just how low IR on a warm car battery is). And my 48V/225Ah bank ran me $1400 about 5 years ago, and is about halfway through service life, or perhaps a bit less than half. To do that on a lithium chemistry would be quite a bit more expensive. Plus, flooded lead acid lacks the energy density to do anything terribly exciting, as long as you give hydrogen generated from charging an "up and out" path. I consider this a feature for stationary storage. And they're almost entirely recyclable (and actively recycled). It's a quite circular economy in the lead acid battery space. Different chemistries have their places. For a somewhat overpaneled off-grid system in daily use, lead acid is still an absolutely reasonable chemistry (as quite a few people here are still observing). [0]: https://www.trojanbattery.com/pdf/datasheets/SPRE_06_415_DS.pdf https://www.trojanbattery.com/pdf/datasheets/SPRE_06_415_DS.... [1]: https://www.trojanbattery.com/pdf/datasheets/SIND_06_610_DS.pdf https://www.trojanbattery.com/pdf/datasheets/SIND_06_610_DS....