Pro 1500 battery symbol blinking

[jeepster_apc]

The Pro 1500 UPS was stored for a few months during renovations. So now switch it on, and the battery charge symbol is empty and blinking.  The faulty battery symbol [with X] does not appear. The mains voltage shows 241, which is correct. I removed the battery and it reads 11 volts, obviously discharged while idle. The user manual does not mention what the blinking means. There are no load devices plugged in. It has been on for several hours and the battery charge symbol is still empty. Batteries are cold, suggesting no charging has occurred. So may I assume the main circuit board is defective?

[jeepster_apc]

Further found that the LCD display is the same if the battery is removed. So then fault is likely a blown fuse or faulty relay....

(posted to wrong sub-forum as it is a few years since I have been here. Can moderator move it to Home/Office sub-forum?)