Hitchcocks Forum

2009 fuel injected 500 bullet that the battery keeps draining. going to test output of the charging system from the bike back to the battery. how many volts should it be putting out when running to properly charge the battery?

14 volts would be nice.

Jaffa et al... For clarity 14 ish volts at the battery when running but with everything else off. If measuring before the regulator then you should be getting wayyyyyyy more volts and it should vary greatly with engine speed (eg up to 40 or 50 volts). After the reg (ie at battery) you should be getting between 13 and about 14.5 ish when running. But... Is your battery goosed - is it actually holding charge?

First check the charged battery voltage with a load on. It should maintain 12v or very near. If it drops right off the battery is kaput.

Interesting reply Dean.

HELLO FROM MY PAST EXPERIENCE OF MOTOR CYCLES HAVING MANY MAKES, IS NORMALLY A RECTIFIER ISSUE, THIS CONVERTS AC CURRENT TO DC FOR THE BATTERY TO CHARGE , INTERNALLY THERE ARE DIODES IN SIDE WHICH CONVERT THE CURRENT THESE CAN FAIL, GET THIS CHECKED . GOOD LUCK

OK so I have this same problem. The old regulator/rectifier was kaput, so I have changed it for a boyer-bransden powerbox from our hosts. I then charged the battery up from the mains and have since ridden for about 200 miles, before the flat battery problem reappeared. The battery charges from a mains charger and holds 12.8 volts. It drops to just under 12 on the electric starter and then returns to 12.8 volts, which suggests the battery (less than a year old) is still OK. The voltage across the battery terminals stays at 12.8 volts when the engine is running and doesn't vary with engine revs. I have tested the output from the alternator to the reg/rect and that seems fine. There is continuity of current between the reg/rect output and the battery. With the engine running, the voltage between the +ve (red) reg/rect terminal and the battery is around 15V and from the -ve (black) to the battery is 12.8V. Is this a weedy new reg/rect or a duff battery or is there something else that I need to check, for example some resistance in the -ve wire to the battery? I'm at a bit of a loss here, but reluctant to give in and take it to a dealer! ...And no, it's not the sidestand switch:)

Have you checked the relevant fuse if any and connectors look for any corrosion, water or poor electrical connexions

Thanks Les, As a short cut I bypassed the bikes wiring and connected the reg rect direct to the battery. When the reg rect output is measured it gives 14.7 volts, but as soon as it is connected to the battery it drops to 12.3 volts, which is the static battery voltage (0.5 volts down from being fully charged before my 80 mile round trip commute). Is this suggesting a duff battery. With all lights on the voltage only drops to 12 and 11ish on the starter button.

If I read what you say correctly it would look like a wiring issue to me, on the later EFI model there is two fuses between the reg rec and the battery even if a fuse is ok it could still be poor wiring to the fuse if there are fuses on your bike, you will need to try and get a wiring diagram and check it through don't also forget the earth side