Topic: Dim Lights - '75 550

[sniper1]

My '75 CB550 has developed very dim lights when not running or just at idle. If I increase revs the light get brighter.

Not running, the battery reads 12 volts. not running with lights on battery reads 5.2 volts.

Could it be a bad battery? Or do I need to look further. Everything was fine about a week or so ago. Nothing else has changed.

[Bodi]

It's definitely a discharged battery, but doesn't definitively say it's a bad battery. A discharged battery like you have is typical of a bike that isn't charging properly... there are many threads here about that. I expect your charging system is running way below design power.

[turboed13b]

How old is the battery? 12v with no load means it is dead. 12.7 is fully charged.

[OldSchool_IsCool]

Low water level in the battery??  Running for long periods below 2500 RPM??  Dirty electrical connections turning valuable power into heat??

The 550 has a notoriously low output charging system.  Running the engine below about 2500 will actually deplete the battery rather than charge it.  Stop and go city traffic can leave you with insufficient juice to start the bike, forcing you to kick start or pop it. 

[sniper1]

Battery is two years old. Water level is good. Typically, I run at about 3,000 - 4,000 rpms. While doing some city riding, I did have to kick start it once last week when it died at a light. I also had to kick start it once after coming to a light after some hard riding (high revs). Not sure what to make of that.
 I put it on a charger for a few hours and battery still reads 12 volts. I guess I will go get another battery tomorrow. I'm trying to get her ready for a trip to the blue ridge this weekend.

[flybox1]

I put it on a charger for a few hours and battery still reads 12 volts. I guess I will go get another battery tomorrow.

+1  replace that battery.
With your new battery installed, and your bike running, you should read 14.5v at the battery terminals with 4000+ RPM