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Can the corrosion on the bolt that holds the negative battery cable to the grounding point on the engine case cause my bike’s charging system to provide less voltage than the battery requires to main a full charge? (I'm trying to figure out how to load the pictures in my iPhone into this thread. I'll have to restart on that effort tomorrow.)

For the last two weekends the voltage that my battery could provide was not enough to start the engine in my 2003 DL 1000. The first time this happened the voltage on my battery per my multimeter was between 11.7 & 11.9 volts, I don’t remember the exact number. This was twenty minutes after a multi-hour ride with almost constant rpms above 3,500 rpm and most of the time above 4,000 rpm. I started the bike, raised the engine rpm to 1,500 rpm and measured the voltage across the terminals of the battery. My multimeter registered 11.94 volts with the low beam headlights burning. I raised the rpms to 3k and the meter read 12.24 volts. I immediately knew that the charging system was not putting out enough voltage to maintain a full charge on the battery with the headlights on.

After pondering the situation for a couple of hours I checked the tightness of the cables to the battery terminals and was able to turn the wrench on each bolt about forty degrees. Restarted the bike, checked the voltage at 3k rpm and got a reading of 12.24 volts again across the battery terminals. I charged the battery overnight with a smart charger, pulled the low beam headlight fuse and headed for home with a buddy following me. After an hour and a half of riding I pulled into an auto parts store. They tested my battery and pronounced it good. It measured 12.74 volts on their tester so the charging system was able to maintain the charge on the battery with the bike running around 4k rpm with the headlights off.

When I got home I had my wife hold the engine speed at 4k rpm and tested the voltage across the terminals again. That time the reading fluctuated between 14.6 and 14.7 volts. I concluded that tightening the battery bolts somehow cured my charging system woes and thought I was good to go.

The next weekend I put the low beam headlight fuse back in the fuse box, started the bike and left for another overnight ride. Long story short, at a rest stop on the way home the starter would barely turn then stopped all together. The battery voltage measured 11.7 volts, pulled the low beam fuse again, jumped the bike off, road home for another hour, checked the battery voltage when I got home and it read 12.2 volts.

I have run the Generator Coil Resistance test detailed on page 7-8 of the service manual and all three readings measured .5 ohm. That was on the high side of the .2-.5 specification but still within spec. Next I measured the Generator No-Load Performance and measured above 77 volts on all three readings. This test was with a mildly warm engine. I don’t see how I could get those voltage readings if the magnets were irregularly spaced on my rotor so I suspect that both my stator and rotor are in good shape.

After reading Canadianfirefighter’s post about his recent charging system woes I learned that he found his negative cable connection to the engine to be loose and corroded. After cleaning up the corrosion and retightening the bolt his charging system started working normally. All problems solved.

My concern is this: the bolt holding the negative cable to my engine grounding point was tight, the battery cable itself was 95% clean and bright, the underside of the bolt head was almost completely free of corrosion and the engine grounding point was free of corrosion. However, as you can see in the picture the bolt holding the negative terminal to the engine case is heavily corroded. Is it likely that the corrosion on this bolt is the cause of my charging system weakness?
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