Sump Pump Backup System

My mom had her house waterproofed on the exterior and the footer system backed up. The water proofing company recommended an interior sump pump. We would like a backup sump pump, but want super reliability. She has a Zoeller M53 sump pump in a crock outside, which will be used as a primary sump pump inside. My brother-in-law recommended the Big Dog Basement Watchdog backup pump, which is nice because it has AC and DC backup as well as a control system that alerts you if there is an issue... however, I've read bad reviews about the battery and some issues with the pump capacity being misleading.

I read a review on Amazon from an electrical engineer who said that he bought 2 primary sump pumps and powered them through a DC/AC power inverter with an auto transfer switch and hooked up multiple batteries in the case of a power failure. This sounds like an excellent idea and seems like it would be more reliable than any current backup system on the market. I am not an expert however and would like advice from you guys.

Is this a better option?

If so, should we have the water proofing company mount the secondary pump higher, so it only runs when the primary pump can't handle the incoming water or in the event that the primary pump fails?

Any comments/suggestions/alternative ideas would be greatly appreciated.

Thanks!