Battery Not Charging on BMW F800GS 2009

Hi There,

This is my first post and here I am begging already!

I was hoping some savvy person can help me sus this out!!

About 3 weeks ago, got off the bike to fill up the petrol, got back on, pressed the button to start the engine.......nothing! After a lot of messing around, I managed to get a battery boost from the guy in the garage and got me started to get home. Right! time for a new battery I think. The next day I sort one out and off we go. I thought my problem was solved.

Well, anyway, about 3 days later, same problem.

Ive done a lot of searching around, a lot of reading. I got a multimeter and did all the tests on the stator/altenator and everything seems fine. 0.2ohm between each pin, no current detected from a grounding tests and the unit is pumping out 70 VAC at 5000 RPM.

Ok, so I move along the line to the voltage regulator and test the outputs, ok, here I am getting less than 1 volt (0.85) with the engine running. This must be my problem right?

I order a new voltage regulator, it comes in the post, I throw it on the bike and go to check the output, now im getting 15V. OK, must be sorted. But then I check the voltage across the battery with the engine running, im barely getting 12.5v . Thats not right as all the guides are telling me it must be at least 13v.

I took the bike to work today, its a round trip of about 90km, when I got home and tested the battery, it was barely over 12v and my battery charger is saying the battery is about half full. I must still have a problem right? Except now, with the stator / altenator double checked, I have not a clue where to look next.

I would greatly appreciate any advice.

Thanks!

If your battery is not fully charged it’ll pull the voltage down.
Stick the battery on charge overnight.
Check voltage across the battery with the engine running. Fully charged and on charge should be 14.4 volts (or thereabouts).
Report back what you find.

AberdeenAngus said:

If your battery is not fully charged it’ll pull the voltage down.
Stick the battery on charge overnight.
Check voltage across the battery with the engine running. Fully charged and on charge should be 14.4 volts (or thereabouts).
Report back what you find.

Click to expand...

Ok, well i had just fully charged it.

Checked it across the pigtail and it came up as 12.85v with engine running

You said your battery charger was saying it was half full, correct?
Put it on charge.
After a few hours, does the charger indicate that the charge level is increasing?
If so, then the battery wasn’t fully charged.
If it sticks at 50% then you’ve either got a bad charger or you’ve knackered your new battery.

Based on what you said, It sounds like you’ve fixed your charging circuit.
My money is on the battery.

I assume you’ve checked condition of battery and earth connections.

AberdeenAngus said:

You said your battery charger was saying it was half full, correct?
Put it on charge.
After a few hours, does the charger indicate that the charge level is increasing?
If so, then the battery wasn’t fully charged.
If it sticks at 50% then you’ve either got a bad charger or you’ve knackered your new battery.

Based on what you said, It sounds like you’ve fixed your charging circuit.
My money is on the battery.

I assume you’ve checked condition of battery and earth connections.

Click to expand...

Earlier today the battery charger was showing the battery at 3 out of 5 bars. I then left it on the charger until it indicated Full. Took about 2 hours.

I have cleaned the battery connectors and there was a brown wire screwed to the engine near the oil filter which I suspected was the battery earth. I removed and cleaned this also.

This happened with me, I ended up replacing the regulator & stator - despite showing good multimeter readings, when I got the stator out half of it was scorched/burned.

Since then I've had no issues.

I did fit a voltage meter so I always know the stator is working when ridng.

D

marcusdav said:

Ok, well i had just fully charged it.

Checked it across the pigtail and it came up as 12.85v with engine running

Click to expand...

If you rev the engine, that reading should increase to about 14.5v by the time you've got to around 4000rpm or so.

Quattroformaggio said:

If you rev the engine, that reading should increase to about 14.5v by the time you've got to around 4000rpm or so.

Click to expand...

There is no mentioning of what year the bike is.

However, the issue has been mainly for the pre 2013 bikes. And if so, run a check to double check good wire connections throughout.
If no connections issues, I'm afraid there is no other solution than replacing the stator, which is a DIY job on this bike..

Chalky723 said:

This happened with me, I ended up replacing the regulator & stator - despite showing good multimeter readings, when I got the stator out half of it was scorched/burned.

Since then I've had no issues.

I did fit a voltage meter so I always know the stator is working when ridng.

D

Click to expand...

Yes, this was it. Changed the stator and everything is working now.

Remarkably easy actually. I was expecting a nightmare of a job.

marcusdav said:

Remarkably easy actually. I was expecting a nightmare of a job.

Click to expand...

Yes, hardest bit for me was getting the old gasket off.

Glad it's all sorted!

D

knutk said:

There is no mentioning of what year the bike is.

However, the issue has been mainly for the pre 2013 bikes. And if so, run a check to double check good wire connections throughout.
If no connections issues, I'm afraid there is no other solution than replacing the stator, which is a DIY job on this bike..

Click to expand...

The 2013 onward models were fitted with an updated flywheel. It had holes in it to allow better cooling by better oil circulation.
My ‘09 bike had a rewound stator which didn’t last long and I then went for the updated flywheel and genuine stator replacement.
That was at around 65,000 miles and on selling at 126,000 I had had no further issues.

Certainly not a cheap fix (about £1300 from memory) but it is THE fix.