also posted on advrider
F650 twin electrical / charging problem - ADVrider

My BMW Exide battery died prematurely, however the dealer didn't have another in stock to replace under warranty. I bought a Taiwanese battery instead. This died after a week. I hooked it up to a charger, and then it was fine.

I finally picked up a new Exide. A week later, I stopped on the side of the road for five minutes, and when I tried to restart, the computer did the diagnostic test, but there was no turning of the starter.

The new Exide was reading 11.4 volts. I had the Taiwanese battery still with me so I changed them over (it had 13.4). No problems, away I went. Stopped for fuel 90km later, and still good. Road into Vic Falls campsite reception, checked in, came out and the battery was dead.

I recharged the Exide on a charger overnight & installed it this morning (reading 13.2 volts). Started the bike with the voltmeter on the terminals. Turning the ignition the charge dropped to 12.4, hit the starter and the bike was running (dropped to 11.2 then quickly back to 12.4). Throttled to 2000, then 3000 and within a few minutes the battery was back to 13.1 volts. It never got over 13.2. I expected with power the battery would read up to 14.4 volts.

Started again, this time under throttle the battery only reached 12.8. After turning the ignition off, battery had recovered to 13 volts.

About to head down the Caprivi (Namibia) but I'm still over 1000 from Windhoek and the next dealer.

Any ideas? I am guessing that because the battery was recharging, though not fully, the voltage regulator / rectifier is dying / dead? Can this be bypassed, or replaced with a car part? There's not much in the way of BMW stuff in Zimbabwe...

The battery doesn't seem to drain overnight. I assume if there was a loose connection / earth that it would drain... the battery only seems to die whilst the bike is running.

Thanks in advance.
Dave

Don't know if this helps, but these were my readings when I had starting problems in the morning. It turned out NOT to be the rectifier but a dead battery:

ignition off 12.6V
ignition on 11.8V
ignition on, lights & handlebar warmers ON 11.6V
engine running warmers off 13.75V
engine running, lights/warmers ON 14V

idle/around 1500rpm: 13.8 V
around 3000 rpm: 13.6V

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