In a blog post from Schneider Electric (parent company of APC), they say that lead-acid UPS batteries "rely on chemistry that makes it hard to accurately predict when they’re going to fail" but "Li-ion batteries always come with sophisticated battery monitoring systems (BMS) that provide a clear picture of battery runtime and health."
I haven't seen this documented anywhere else, although I have experienced unexpected UPS failure many times myself - even with UPS models that have a "replace battery" indicator. Having had too many UPS backups fail without warning, I am looking for a reliable UPS: either a lead-acid UPS with a battery meter (not just an indicator LED), or a UPS with a lithium-ion battery.
Can someone provide me with more information about the reliability of lead-acid batteries?
The BG500 (500VA, 300W) is lithium ion.
You'll note that the next level up, the BG700G (700VA, 420W) uses lead-acid and is cheaper though lacks network manageability. Since the battery lasts 3-5 years in a UPS environment, those who need reliability swap 'em out after three. The latest SmartUPS' automate this approach and proactively warn that the battery should be swapped out even if it hasn't failed (see this post).
An important consideration is that most lithium battery systems use individual cell battery management, whereas lead/acid batteries very rarely use any individual cell monitoring at all (most designs prohibit effective monitoring). One exception is the use of FLA (flooded) lead acid batteries with monitoring of individual cell specific gravities of the sulfuric acid. This is tedious and generally only used by serious off-gridders, or industrial users - most auto batteries are designed to not access the electrolyte. The UPS AGM batteries have no means to monitor individual cells, to do so would add unacceptable costs (they are very cheap in cost and construction!). The maturing electric vehicle industry is the "master" of manufacturing, monitoring, managing, and protecting large number of lithium battery cells in series - any one of which can take down the entire battery! IMO, the lithium battery industry will continually get better at this. Imagine the next gen of EVs with 800 volt DC batteries - that is approx 200 "cells" in series. That is going to require some serious "management".
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