APC Back-UPS RS 800 flashing the overload and replace battery lights
This is indicative of a board failure, this is not a battery problem. This could have been caused by a surge or by aged components. This is not repairable, the UPS will need to be replaced. If your battery is still fairly new, you can save some money and make use of your batteries by buying a refurbished core (the unit itself) without the batteries. If your batteries are over 3 years old it’s best to either buy a refurbished br800blk ups with new batteries or buy a brand new UPS.
If you need a refurbished core without the batteries, get in touch with us to check availability.