Sump Pump issue

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I have a Zoeller M53 sump pump with Zoeller 507 battery backup with the Basement Sentry. I started getting an alarm some weeks back with the red AC light flashing. I opened the cover and lifted the float and the main pump comes on. I had the company who installed it come out and they said everything seems to be working right, maybe it was the battery. When I shut off the alarm for 24 hours by holding on it for 3 seconds, it showed 12.54V with the old battery. Online says if it goes below 10.78 I believe it was that it will alarm but mine is higher and still alarms.

I bought a new battery and that started out at 12.78V and even though the red AC light still flashes, it did not alarm right away but now it is again after a few days. The voltage has dropped from 12.78 when new to 12.57 over a 2 to 3 week period, according to the Basement Sentry as of tonight. I called Zoeller and was told that it alarms for 2 reasons. The battery and if it is the battery, the alarm can't be turned off until it is resolved or the backup pump is running. Told him the backup pump is not running and he just kept going back to the backup pump is running. It definitely is not, I was disappointed with the help from Zoeller.

The company I had install it, has recently said that it might be the battery backup system since it is 5 years old and it will cost $1200.00 dollars. I did a search online and it says that battery backup systems last 3-5 years, even if not used much, which mine has not been used at all as far as I know. We very rarely lose electricity and when we do, it usually goes off and comes back on almost immediately. I have the following questions.

Isn't there any way to test the backup system to know if it is bad?

Isn't there any way to test the whole system for problems in general?

You have to replace the whole battery backup system including the backup pump, you can't replace individual parts?

Anyone have any ideas as to what could be wrong, or what I should do next?
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6th clinical trail chemotherapy 5/15/24
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Orlando, Florida
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