As long as you were happy with the performance when it worked correctly and you need nothing else.
Buy a new one, it is not worth buying a replacement battery usually.

Or try this one for a few dollars more..
Here is a different apc ups rated at 1500va but has sinewave correction in addition..
This gives you cleaner power to the electronics devices.
APC BR1500MS

It has slightly different configuration on number of outlets.

You can't go much bigger without a huge price jump.

FYI,
Not all ups units are the same.
Your model and the one I suggested are consumer grade UPS
The model you have switches to battery power during a outage so some electronics may see the bump in power.
It depends on how fast they switch to battery.

There are online units than are always on battery and there is no bump at all during a outage. But again they are pricy.
And when the battery goes out the unit does not put out power to the outlets at all.
Last time I priced one they were around $1500.00

Last edited by Ruben; 07/13/2020 1:21 PM.
There is no such thing as stupid questions , Just stupid answers.