BX1500M Empty Charge Icon Flashing

[JRF]

Got a BX1500M from a friend that closed his shop last year.

1. "online" & power plug icon is on

2. load icon is on (no load)

3. the long battery "charging" icon shows no charge & is flashing

4. there are 2 short beeps on every other flash of the charging icon

5. No errors shown

6. Neither the battery or battery with an X is showing.

I pulled the battery and held the power button & no change in status.

When I pulled the battery, it was reading 14V

I left it charging for about 20 hours and no change in the charging icon - no charge indicated & still flashing

I pulled the battery and it now measures ~18.5V

I also noted that it gives the exact same indication if the battery pack is not installed. 

There is nothing in the user manual that describes the icon condition noted above.

Side note... although I have years in electronics and tech support, it is useless without schematics or other such information on how this unit works. I'm speculating that it may be an internal problem with one of the (dual) battery packs, but reluctant to buy a new battery pack (due to cost) without some sort of confirmation, especially if it is due to a defective UPS instead of a battery.