Battery backup periodic beeping - APC Back-UPS ES 350 - UPS ( external ) - 350 VA - UPS battery lead acid - 6 output connector(s) (NEWITEM13161548) UPS System

as long as garage door is powered(plugged into outlet), then with a removed battery backup or a bad backup battery, the unit will beep to alert you to the issue. replace the backup battery with a new/good one.

if it is about a smoke alarm with a battery in it, when the alarm beeps for no apparent reason, it is a bult in indicator that the battery is flat or approaching a low voltage and needs replacing
If it still beeps after replacing the battery have it checked out as a fire alarm is critical for your safety

Is there a phone number on the control panel?
Is there a backup battery that may need to be replaced?
If there is any contact information available, call to get the manual, etc.
Gary

Usually that indicates a low battery charge or bad battery. Make sure you do not have the battery backup side overloaded with too many devices. Do not plug inductive loads with motors or heating elements into the backup. Turn the device off and unplug anything that is plugged into the bachup. Plug the battery backup into the wall with nothing attached and turn on. Wait 10-15 minutes. this will charge the battery. If beeping continues after this with nothing attached, you likely need a new battery or the control/monitoring system is bad. If beeps stop, reinstall and do not attach more wattage than the unit can suppluy

It appears that the 5 year period of inop has drained the battery beyond recharge capability. Try replacing the battery.

More than likely the battery's are not accepting a charge due to age or not being charged for a long period of time.
If the ups continues to beep after leaving on overnite, the battery's will have to be replaced.

I have gone through a few UPS, Im lucky to get 3 to 4 minutes if my power is cut.
I think most people plug too much into the UPS sockets.
The Battery backup protected sockets cant take the drain from everything over a prolonged period of time.
The nature of rechargable batteries means that when plugged permanently into a power supply they get damaged (li-on batterys especially).
Im afraid i cant help with this UPS, looks like you need a new 1.
I now only have my PC/Monitor/modem and router plugged into the UPS protected sockets.
Speakers / printer and other stuff are plugged into the unprotected sockets.

check the user manual, but that battery will need to be charged for a period of time before it goes full load.

Is the battery connected internally and the unit pluged in the wall,by the sounds of it ,You may have a bad battery.Check to seeif infact it charges.
Good Luck