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Starter failure following jump start


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Last night I had just returned from a 3 day business trip to Vienna and was preparing to ride out from the bike park at Heathrow Airport, when - horror of horrors - the battery was flat.


While I was pondering what to do, another user of the bike park told me he saw my lights looking pretty low the previous day. Obviously I had inadvertently left them on at the time I parked, and the battery had slowly died. Normally the battery is perfectly OK as I use the bike every day to commute to work.


Anyway, a quick call to the BMW Emergency hotline, and I had a service truck restart the bike by jumping it from a 12V battery. It fired up OK, and my 25 mile trip home to North London should have been enough to recharge it.


However, first thing this morning I tried to start the bike and I got this horrible rapid chattering noise from the vicinity of the starter motor. There was no sensation that the motor was actually trurning, but rather that some electrical problem was at work.


My gut feel is that the battery has not re-charged sufficiently, but out of curiosity, and before I start investigating it, do you folks know whether the jump start process may have been the cause, and that somehow I have burned something out?



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I would doubt very strongly that any damage was done. Depending on your average road speed and load on the charging system the ride home may well have been insufficient to properly charge a dead battery. Try giving it a full charge with a external charger and see if that cures the issue. If not your battery is likely on its last legs and a replacement should cure all your problems.

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The loud chattering is the starter solenoid engaging, the starter motor load causing the battery voltage to drop and releasing the solenoid. This lets the voltage increase enough to pull in the solenoid and so on.


Causes? Low battery charge is one possible cause, as is loose/corroded battery terminals. My money though is on the battery having died. I say this because the worst condition for a lead-acid battery is a slow-discharge to totally flat. This leads to sulphation and possible warping of the plates. The build up of sulphates on the plates increases the batteries internal resistance and can cause the exact symptoms you describe. I would bite the bullet and replace the battery.



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Yure BMW electrical system doesn't know where the 12VDC comes from and doesn't really care. Jump starting a dead BMW motorcycle does no more damage that jump starting an auto......in otherwords...NONE


But, before your discard the battery, try a nice long, slow charge, 1 Ahr for 20 hours.


Be sure to fill up the cells with DI water. Also monitor the water as the battery is being charged and keep the cells topped up. A slow charge may provide you with another year of battery service....I would not be so quick to discard it........the attempted fix is very cheap and may surprise you.....remember, slow charge......

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