Need help with RTP!

So I am a new guy here, but not new to BMW RT's. However I have a bike now that has me perplexed. I have a 2009 R1200RTP, and this bike started randomly throwing a battery light. If it comes on then it stays on. It always comes on right after start up, but sometimes it comes on and sometimes it doesn't. I bought a brand new battery from my local dealer. I noticed the aux battery wasn't hooked up completely. Now it is and it's fully charged. Both batteries hold a full charge. When running the volts are registering around 14-14.25 on both batteries. Again they both remain fully charged. Sometimes it comes on and sometimes not. I've tried disconnecting the aux battery and it still comes on. The dealer is at a loss. Any ideas? Thoughts? I'm lost at this point.

So I am a new guy here, but not new to BMW RT's. However I have a bike now that has me perplexed. I have a 2009 R1200RTP, and this bike started randomly throwing a battery light. If it comes on then it stays on. It always comes on right after start up, but sometimes it comes on and sometimes it doesn't. I bought a brand new battery from my local dealer. I noticed the aux battery wasn't hooked up completely. Now it is and it's fully charged. Both batteries hold a full charge. When running the volts are registering around 14-14.25 on both batteries. Again they both remain fully charged. Sometimes it comes on and sometimes not. I've tried disconnecting the aux battery and it still comes on. The dealer is at a loss. Any ideas? Thoughts? I'm lost at this point.

Afternoon Robert

We could use a little (actually a lot more) information on your problem.

Is the charging light ON when you are seeing the 14-14.25 charging voltage?

Does the light only come on after a start but then eventually go off?

When the light comes on does it stay on throughout the entire key-on period.

The more (exact & complete) info that you furnish the better we can direct you to your problem.

It might just be a slipping alternator belt (original 1200 belts were known to be a bit on the loose/slipping side, especially when wet or right after a start up).

Yes the charging (battery) light is on when seeing the voltage. It only comes on right after a start and never goes off. It'll stay on during the whole time the engine is running. Even at higher speeds. It will not go off until the bike is turned off. I thought it might be the belt, but if it was wouldn't it go off after a while? If you turn it off after it comes on, then start the bike back up it may or may not come on again.

Regarding the aux. battery, do you know for sure it actually is hooked up to anything ?

When the bikes are retired, the aux. battery, which controls the police lights and the radio is often disconnected or removed as that's all it does from the factory. Some motor shops may wire an accessory to it but it has no starting or running function at all.

The bike will continue to attempt to keep it charged if it's hooked up even if it has a dead cell.

Many times, the aux battery cables are unhooked and taped up when the bike is taken out of service.

It is still hooked up. When not running the aux battery is at 12.8 volts. When running it's at 14 over 2000 rpm. I don't know if the aux battery is hooked up to anything except the horn and emergency flashers.

Yes the charging (battery) light is on when seeing the voltage. It only comes on right after a start and never goes off. It'll stay on during the whole time the engine is running. Even at higher speeds. It will not go off until the bike is turned off. I thought it might be the belt, but if it was wouldn't it go off after a while? If you turn it off after it comes on, then start the bike back up it may or may not come on again.

Afternoon Robert

With the info you just furnished this is gong to a tough problem to solve over the internet.

The RT-P has conventional charge input for the primary battery with a delayed (raised RPM) charging of the secondary battery (as from the factory). But there was a CIP to flash into the ZFE that allowed the secondary battery to charge all the way back to idle once the RPM's met requirements to start secondary charging. This goes through & is controlled by the ZFE chassis computer (this might have nothing to do with your problem, just mentioned here to show the complexity of the 1200RT-P charging system.

A quick guess on my part would be to check the BLUE wire going to the alternator as THAT is the wire & circuit that the ZFE uses to energize the alternator & also uses to determine IF the alternator is actually charging. The alternator will start charging on it's own without that BLUE wire & ZFE starting charge but the charging won't start on it's own until a raised engine RPM.

So make sure that the the blue wire is firmly connected to the alternator & that the blue wire is not cut, grounded, or has ANYHING else connected to it. (this would be MY starting point anyhow).

The ZFE uses the CAN system (CanBus) to tell the dash module to light the charging light so make sure that you have no unconnected CAN terminations (loose connectors with CanBus wiring going to them. Any unconnected CanBus termination MUST be either connected to a module, or terminated with an RFI terminating resistor. Being an RT-P this is not an easy thing to verify as I am not sure what all (police-equipment-wise) has CAN access.

Either of the above mentioned could still allow proper battery charging even with the charge light still illuminated.

Then there is the remote chance that the alternator regulator is the cause on the charge light being on (in rare instances the regulator electronics can still charge OK but still put the charge light on). Or even a shorted alternator internal diode can cause the charge light to light (will have reduced charging output but could still charge the batteries OK at low circuit loads)

Then there is a the very remote chance of something being wrong with either the ZFE or the dash module that simply lights the charge light even though it is charging correctly (how a person would find this problem is difficult to say as both ZFE & dash module are not easily swappable due to needing to be flashed into the bike's main electronics'.

Last thing_-- Are you SURE that your yellow light is indicating a charge problem & not some other issue?

Wow! Thank you so much for the information. I really appreciate it. It is throwing a red light and the battery symbol is coming on. It comes on sometimes with a start. I have no dim lights or anything even with the light on.

As weird as it is, the bike recently sat for 2 1/2 weeks without being started. Went out to it this evening, it started right up and the battery light isn't on. Lolol