I have the APC BACKUPS 650 with a similar problem...however, it won't turn on the battery backup outlets, even with the unit connected to good 120VAC power. Just makes a ringing noise, which sounds like an inverter, but no power comes to the outlets. Only 3.45 volts are trying to charge a 12 volt battery. I took the battery out and charged it on my car charger on the slowest setting and it seems to hold a charge. After charging I can connect it to the UPS and with the unit unpluged from the wall, it make the same ringing noise. The green power light comes on, but pushing the on button does...