LiFePo is maybe 10x the lifespan of a normal Lead-Acid battery, if you're cycling it several times a day. A car battery for instance will not do very well in this test. But I'm talking about deep cycle Lead-Acid batteries, cycled every day or couple of days down to 70% capacity (so using 30%). This is a fairly typical workload if you're (for instance) using it as a backup for solar panels. Under those circumstances, the LiFePo battery will die from time elapsed probably about the same time as or maybe even earlier than the Lead-Acid battery dies from cycle count.
Well that was interesting, I wasn't aware that flooded lead acid was that much better and that AGM just plain sucks in general, which was also my observation dealing with UPS batteries.
Still, I would've expected that ever increasing self discharge would've made them far worse in comparison since it gets worse as the batteries age and you can end up losing major amounts of charge to it. Not sure if that's not as much of a problem for flooded as it is for AGM but I haven't heard it mentioned in the rundown.
Kind of. Consider solar panels. A lot of the time, you'll be using around 30% of the discharge capacity to keep you overnight. However, some days will be cloudy, so you might have to use more of the capacity.
In this situation, a Lead-Acid will have the full capacity that you bought, but will age like you're using 30% of the capacity most of the time.
LiFePo can last longer than Lead-Acid. It depends on the usage.
LiFePo has a very high maximum cycle count. But after ten years, they'll die anyway. The only way that you can actually achieve a cycle count as high as the specification says is if you're cycling the battery two or three times a day, which I can believe if you're doing grid-levelling, but not if you're providing backup for your solar panels.
For lead-acid batteries, be aware of the difference between normal lead-acid, which are optimised for standby operation, and deep-cycle lead-acid, which are optimised for long life under regular cycling. Normal lead-acid batteries will die very quickly if cycled - they're designed to be charged all the time, and drawn on for very short period, like a car battery or a UPS.
Deep-cycle lead-acid batteries age by cycling, in contrast to LiFePo, which age by elapsed time. Their maximum cycle count is much lower than LiFePo, but if you're cycling them every couple of days, like in an off-grid solar project, and you're avoiding draining them below around 40%, then they can last 10 years.
So, if you want to cycle your batteries two or three times a day, then LiFePo is going to last a lot longer than Lead-Acid. But if you're cycling every couple of days and limiting the drain, then they can last about the same amount of time. It depends on the usage.
What helps with Lead-Acid is because it is that much cheaper than LiFePo, you can buy a larger capacity Lead-Acid battery for the same or less money, and then for the same performance requirements that larger battery will be drained less and at a lower rate, and therefore be less stressed and even last longer.
I think we don't use Lead-Acid as much as we do for several reasons:
1. Lead-Acid batteries have a reputation of flaking on us after a depressingly short amount of time. But that reputation has been earned from normal Lead-Acid batteries, not deep cycle ones.
2. People get scared by the lead in them, and how lead is toxic and we should be stopping using lead in everything. But really, lead in these batteries is not a danger to us, and Lead-Acid batteries are one of the best recycling success stories in the world. That lead isn't generally getting out into the environment. LiFePo batteries are much harder to recycle.
3. Electricians recommend installing expensive stuff, because then they get a bigger commission.
4. Lead-Acid batteries are commodities, but LiFePo batteries are new and exciting, and have aggressive marketing.
5. Lead-Acid are bigger and heavier for the same capacity than LiFePo. So, a LiFePo installation is going to look prettier in a nice consumer unit and be easier to install. They're heavy enough as it is.
This is very insightful, thank you. I guess for price per kWh, lead-acid is also still unbeatable. And as you mention, deep cycle can give good lifetime as long as you don't go below 40%. I see deep cycle batteries come in all kinds of voltages though - is there a preference? I've seen huge 1000Ah batteries with 4V or 6V.
