I have a FiOS Verizon MI424WR wifi router that is connected to the Internet via a ONT which is power by a BBU that status light turn to red ever 4hr and I hear a very mild buzzer noise coming out of the BBU. I replaced the battery with a new one of the same 12V 7.2Ah SLA from Homedepot. I charge the new battery, even thought it comes precharged, with a Auto Car Battery charger that could charge a battery in 4 hrs if I put it on the trickle charge mode (with a 2amp setting) or if I put it on the 10amp it charges even faster. So I got the Internet connection back and however, the new battery also drained in about 4hrs and the ONT BBU status light goes red. So I find no problem with the old battery and now I recharge them one while the other one is working and cycling them every 4hr.
Have anyone experinced such a problem and wonder how that resolved calling the FiOS repair service?
The BBU shold not make noise unless it is the beep to let you know the battery is dead. Have you rebooted the system? remove the battery and pull the plug. Will the service work without the battery in? (it should) If not then the BBU is shorted out. that might explain the buzzing noise. You may need a tech to replace BBU.