- Wed Jun 12, 2019 8:43 am
#83499
Take the key out and put it in your pocket. Get an multimeter and connect it in SERIES with the battery positive.
On most modern bikes, you will see a spike in current as it is connected followed by it dropping (because of the presence of semi-conductors). You are measuring earth leakage, a very small amount is normal. So for example, I checked my wifes CBR600 the other day because the battery was flat and it had a leakage of 9mA. To put that in perspective, it would take it over a year to flatten the 12Ah battery it has fitted at that rate.
So low leakage, probably not a problem. Higher leakage, start unplugging things one at a time until it drops... Start with the reg/rec.
There's a caveat. I said to put the key in your pocket because most multimeters only read in a milliamp scale. If you power up the fuel injection/lights with the meter connected, it'll pop the meter fuse. If you have an unusally high earth leakage or something is coming on by itself, it could also pop the meter.
Further to the adive haggis gave. One way of testing the battery itself is to charge it, leave it on the shelf and check the voltage every few hours. It should settle at a steady voltage in the 13-14v region. Another option is some better equipped garages and motor factors will have a battery load tester. This stresses the battery by making a huge demand on it and looks at how quickly it recovers.
The following is just a partly related anecdote that shows how weird these things CAN be. A friend kept finding his bike with a flat battery (it's a huge diesel car engined bike, so the battery is enormous). One day he found the bike had been moved and had a flat battery. Now this is odd because it was locked in a shipping container in his back garden.
He also has CCTV which he checked and sure as hell, his bike, in the middle of the night, started rocking about by itself. This happened three or four times up to an hour apart, then it rolled forwards about 4 feet and stopped. So do we need a mechanic or an exorcist here?
It turns out, there was some cracking on the bundle of cables leading into the solenoid. In particular, on the main live feed to the ignition switch AND on the trigger wire for the starter solenoid. Enough damp had got in that a current started to flow between the two wires, activating the starter motor. The movement then separated the wires slightly, breaking the circuit. This cycle was going on for most of the night, activsating the starter for half a second at a time and flattening the battery. This particular night, he'd parked the bike in gear and it made contact for long enough to roll the bike forwards on the starter motor.