Clip an ammeter on the battery lead.

 

Lead acid batteries actually are "fixed energy" devices for life span. The deeper you discharge them (in terms of A-hr), the sooner they go away. "Deep discharge" batteries are built to allow deeper cycling over their lives, but use still equals life span for these guys.

 

For my travel trailer, the house battery on my boat, backup power for my ham station, I use 100Ah Sealed Lead Acid (AGM) batteries designed for UPS service. I happen to have a source of these that are removed from commercial service after they get two years old. They typically have a capacity of about 85Ah when I get them. I use them for about three years and discard them when their capacity goes below ~50Ah. To get three years, I constantly float them per the manufacturer's instructions (13.5V to 13.8V, depending on ambient temperature), other wise, just sitting around, they go dead in six months to a year, and cannot be recovered.

Check with local government or businesses that have standby power systems. For critical applications, they routinely remove from service batteries that still have a lot of useful life for a hobbyist.

__________________
Mike ML.

 

BATT. BACKUP TIME = AH[capicity of batt.]*12[batt voltage]*N[no. of batt.]*0.8[power fuctor]*0.9[eficiancy of inverter]\ VA[ o\p load ]

 

Your 24Ah battery is rated to provide only 2.4A for 10 hours or 1.2A for 20 hours.
With a load of 24A then it might last only a few minutes.

__________________
Uncle $crooge

 

Curious as to the manufacturer and model no. of your UPS batteries. If I could be so bold as to ask; are they from a telecom co.? and how much did they cost? Five years of service is very good for deep discharges, more than double probably than a standard flooded lead acid battery.

I have a 100ah Deka AGM battery in the pickup camper and it has a very low discharge rate. It was bought new and cost an arm and a leg. Left the battery in a full charge condition 4mos. ago (about 12.9V). After reconnecting the battery, turned on the hood fan for a couple of minutes. Rechecked the battery voltage and it was 12.6V. Normally, they should have a very good shelf life, or low self discharge rate.

 

Can i have a diagram?

 

is there a cheapest inverter?