Sump pumps are one of the most boring parts of home ownership. Until that one storm comes and suddenly they’re interesting.
After losing power one time this summer, I got paranoid and decided to build a battery backup. Home Depot had the basement watchdog systems, but they seemed high maintenance and I wanted something that would let me be lazier. I went with a LifePo4 battery system, that will (hopefully) get me 10 to 15 years. The battery charger has a float/storage mode so it can stay on 24/7. Doing some test runs, I think I can get about 400 cycles out of the battery before it hits 0%. I added some additional safety features (DC circuit breaker, GFCI with auto-on, Lithium fire extinguiser, etc), and added some battery powered lights and a basket of hand tools, so in the event the power goes out in the dead of night, something goes wrong, and I have to get my feet wet, everything is there ready to go.
Watchdog can lose all things out of one of the following lines and still run, and it will let you know if either line fails with an audible alarm.
120v->Fuse->120v motor->120v impeller->120v float
or
12v battery -> 12v Fuse -> 12v motor->12v float
The only shared point of failure would be a crack or hole in the exit line
The 12 and 120 sides are completely seperate except the water exit path.
The 120v side doesn’t get anything from the “control box,” it’s just a float pump.
If you filled the some faster than the 120 could pump, they’d both run at the same time. (and it would complain audibly about it)