BMW R1200RT/R1250RT Forum

I was being impatient, I guess....


Overnight it has charged up to 14.4V (which the manual for the charger says is the point that it stops charging), the 'full' light is on and display says 100% and a trickle charge of 0.2A (not sure why there's any current if the battery is fully charged).


So I've answered my question 2 from my last post but still not questions 1 (sequence for connection) and question 3 (why the display on the charger changes to say 100% charge with the 'power' and 'full' LED's lit if I disconnect the power to the charger and leave it plugged into the aux socket during a charging cycle, with the bike ignition switched off). Any thoughts still welcome.


By the way the bike is only a couple of days old - a replacement for the one with all the gremlins I had for the past 3 months . Hence the query about taking so long to charge up. I would have thought a new bike would be delivered with a fully charged battery (1 mile on the odometer when delivered to my home)?

1 also have the latest BMW charger.
Don't think there is any sequence necessary to get it working.  Just plug it in to a switched off bike then turn on the mains.
Mine starts up as follows.
On switching on mains if its plugged in the bike you get "No battery" for a couple of seconds.
It then slowly starts charging until you get to  100% full.  This takes anywhere from 30 minutes to a couple if hours depending on battery state.
On getting to 100%  it shows that for a while before switching off the LED display and you get a flashing stand by light.  The unit then goes cold.
I cant see any reason for leaving the unit plugged into the bike but disconnected.  Try disconnecting it from the bike but leave the mains on, it should show No battery.

Thanks RTMan - will check that out

Hi RT Man it works exactly as you said except it got to 100% with the 'full' LED lit and has stayed like that with  a 0.1 A charge (occasionally toggling to 0.2A charge) for over 12 hours without going into the final 'sleep' state you describe. Any more thoughts?

Yep.  You havnt got anything attached to the back of the socket by any chance, or any electrical accessory wired in somewhere.  It sounds like something is not fully shutting down.  If not try the other socket if you have 2 fitted.  Last resort, ask for another charger.

RT Man, you've been really helpful here so thanks. After I got your last response I tried the charger connected directly to the battery and it all works fine as you'd said it should (see photo). Put it back into the aux socket and it never gets to 'maintenance'.


I guess there are two or even three(?) possible conclusions:


1. The charger works when connected directly but it's circuitry that interfaces to the Canbus system is faulty... or...


2. The charger is working fine but as you suggested the bike is drawing current from the aux socket...


.... or maybe??


3. It needs to be connected to a second aux socket as the main aux socket always has a current draw(?)


I don't have a second aux socket so can't try that. At least, I don't think so... It's an LE but I didn't stipulate an extra aux socket when I ordered it and can't see a second socket. It's a brand new bike so I wonder what is drawing the current. Does yours work fine in the main aux socket? Cheers.

The rear socket is on the left under the pillion grab handle.  I  suspect though  with no extras strapped on it will react the same.  You probably need to get your dealer to plug in and check the system. Bit of anorak info. The RT has Linbus which apparently is a simplified but more efficient Canbus. 

Thanks for the help again...

Well knock me over with one of Mrs Miggins' pies. You're right, there's a second aux socket hiding (very well) there!

However, you're also right in that it's exactly the same result with the charger - never goes into 'maintenance'. I'll get it checked out at it's first service.

I've just got this bike as a replacement for the last one that had electronic/electrical gremlins that they couldn't find. I hope this is not going the same way, although on the face of it, this seems like a minor problem  that doesn't affect normal performance......(I hope that's not famous last words)    :wonder:

Thanks also re Linbus versus Canbus.  8)

And until then don't let the battery  go flat. They are never the same if that happens. Best of luck.

Silly question but after the problems with my first RT (which I had from new for six weeks before sending back with electrical gremlins including a charging problem that led to a flat battery and after that things went down hill), do you mean the battery or the bike is never the same after a flat battery?

The battery

Just purchased an Optimate 4 from FC Moto in Germany 69.00€ about £54 compared to UK £79 plus postage. Sorted.

Steve, over the winter I installed a Garmin 660 and took my power from the factory plug behind the headlight. After that, using the same charger you have I never reached 100% going through the powerlet sockets. After reviewing the wiring schematic I found that both sockets and that switched GPS power source all shared the same ground. Something in the GPS kept the charger from going into sleep mode.


I gave up and have been using a regular old fashioned standard battery tender wired direct to the battery ever since and have had no further problems. My battery actually seems to crank stronger when I roll the bike out after it's been sitting than it ever did before, and all electronics are working without any hiccups.

Firenailer, why would you charge your bike with the Satnav in? I suppose you could say why not? I have just purchased an Optimate 4 and I have never used a battery maintenance accessory before as I found I was always riding in all weather duvets my job, but since retiring and post op the bike is idle at the moment.


The reason I purchased the optimiser is a comment on this thread: RTman10 ... and don't let it go flat it's never the same again. Since he is a Wise Old Owl I take what he says seriously. So before I even consider starting the bike I am going to plug in my Optimate 4 when it arrives.

Firenailer.  You don't say what type of charger you plugged directly into the sockets.  Remember your bike had Canbus/Linbus wiring which requires a Canbus compatible charger to work properly.  The latest Optimate charger are OK as is if course BMWs own. Anything else can cause faults to the system.