A while ago I asked about backup battery power for a primary AC sump pump Is this 12V battery backup set up correctly for a 120V sump pump? That and other questions make it clear to me that using a secondary DC sump pump is a more efficient, safe, and reliable automatic backup option.
Now that I am looking for secondary DC sump pumps, I see most use lead acid batteries. The ideal - for reliability and safety in a house with kids - seems like maintenance-free sealed AGM lead acid batteries. However, I have a 100Ah 12V LiFePO4 smart battery from Renogy that is now largely unused. I got it a few years ago for an off-grid project that LiFePO4 was more appropriate for but that project evolved and doesn't need this one.
Since I already have this high-quality battery and LiFePO4 is considered very safe and high performance, I wonder if I should just use this with a DC backup sump pump. There are three considerations I'm looking for more expert input on:
Safety: Am I right in thinking LiFePO4 is safer than AGM lead-acid? On the one hand, not having lead and sulfuric acid in the house seems like a plus, especially with kids around. On the other hand, I hear about lithium ion batteries having runaway heat issues leading to catastrophic fires. But my understanding is LiFePO4 is safer than lithium ion and is in fact safer than AGM lead-acid as well in terms of fire risk.
Reliability: This is a big uncertainty to me. When I used this LiFePO4 battery, it was with a high-quality charger Victron BlueSmart IP65 Charger (12 VDC, 15A). With DC backup sump pumps, quality kits include a battery maintainer that serves a few key roles the Victron charger does not. While they both trickle charge, the pump kits are designed to trickle charge and float a lead-acid battery, and the pump kits have automatic test features that send signals to a monitoring device. The kits vary but the idea is the same: test the backup pump, show on a monitor that the pump is working or not. With a LiFePO4 battery instead of a lead-acid AGM battery, does this kind of reliability go out the window or introduce problems in charging?
Efficiency: I figure energy efficiency is equivalent since DC power is DC power from either battery, and weight is not a concern here. Economic efficiency is what I'm wondering about. I already own this LiFePO4 battery, but it looks like I could sell it online for $400 or so and a 100Ah 12V AGM battery would run me about $200. So I'd weigh the sunk cost (I paid almost $800 for the battery around the pandemic), but AGM battery seems more cost effective today.
I spell out this criteria so this is not as opinion based. Am I assessing these criteria correctly, or am I missing something in terms of safety, reliability, and efficiency? Thanks for your input!
