BMW R1200RT/R1250RT Forum

Morning all




Curious, came to get the bike out yesterday after 2 days sitting there , and shocked my battery was flat..


Only thing I forgot to remove was my sat nav... could this of drawn enough to flatten it??


Very odd.  Did 300 miles yesterday, no issues, stopped for 45 minutes. 


Started fine this morning. 


Put my optimate on to check battery, and needing charging as it showed amber..


Now the only other thing I have added is my Ezcan which controls my front and rear auxiliary lights. 


Any ideas??

It wouldn't have been the Nav VI. Once the bike is off the Nav goes into Standby mode, and although that will run the Nav Battery down, it doesn't draw any power from the bike. Again the Hex should shut down with the Canbus shut off, but even so, it wouldn't draw enough current to drain the battery. Think I would be looking for a bad earth or connection not allowing the battery to power up the bike. If it happens again, check the battery with a meter to see if it is actually flat. So not a lot of help really - sorry

Is the sat. nav. powered from a switched live or wired directly to the battery.

David. wrote: Is the sat. nav. powered from a switched live or wired directly to the battery.

Good point, but if it wasn't a switched live, wouldn't the nav stay on all the time.

Casbar wrote:
Good point, but if it wasn't a switched live, wouldn't the nav stay on all the time.

Yes. The Nav only stays on whilst it detects a power source, once that power source has gone, it offers you the choice of shutting down straight away or shuts down itself after the countdown clock of detecting no power source. I run a Tomtom rider V2,400 range and BMW Nav6, and they all stay live whilst connected direct to the battery but shut down when the power source is cut.


ps. Possibly alterable within the settings?

Have you any idea how old the battery is?  Could well be the battery, modern batteries unlike those from years ago give no warning of failure.  The only real way to check a batteries state is with an electronic battery tester, my bike is fitted with a tracker which I have programmed to give me an alert when the battery voltage reaches the set voltage.  This triggered last week despite being used all weekend so I guess it is time to think about replacing the battery.  I speak from experience being a truck technician but we still have battery failures during the warmer weather.

Thank you all.  Very good points on from all.  I have no idea how old the battery is, I can only assume it’s the original one from new, so I guess having no paperwork saying either way, I can only assume. 


The sat nav does power down once I switch off the bike, as does the Ezcan ...


So maybe I need to check the terminals and make sure they are okay first, then check the battery , so I will get it tested. 


Thank you all. 


Update...did another 150 miles today...and checked battery which was showing fully charged...so I guess it’s charging ok. 


I will check status in the morning..then report.  But if it shows low again, I will get it tested and results of that, I may need to buy a new battery. 


Thanks all.  Much appreciated

Do you have a multimeter to check it?
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Yeah I do.  I will check it later. Cheers for that .. much appreciated

If it's an old battery that's showing signs of failing would it not be better just to replace it anyway? Next time it might let you down away from home and then its a pain in the a*#e to sort out.

Tested the battery.  No ignition it was reading over 12 volts.  Started it reads over 14 Volts.    So battery seems okay.  So now I’m bloody mystified. Hmmm

Davef1uk wrote: Tested the battery.  No ignition it was reading over 12 volts.  Started it reads over 14 Volts.    So battery seems okay.  So now I’m bloody mystified. Hmmm

Car and bike batteries often give an unusually high reading unless under load, so a multimeter may not be accurate. I proper car battery tester has a big resister to supply the load.


Basically what you need out of a battery is Watts not Volts, with no load it outputs the correct volts, when you put a load on it there is a draw of lots of amps so which the watts output cannot support so it drops the volts. That's why batteries are defined by Amp Hours.


The voltage when running will be the input from the alternator

Perform a cranking voltage test

You can perform a test with the battery under load (working) to get an idea of the current flowing through it. Hook up your DVOM in the same manner you did for the standing voltage test, and have an assistant thumb the starter. While the starter is spinning, observe the voltage. The starter should be running at normal speed. A good battery should not drop below 9.6 volts over 10 seconds or so.

Cheers guys. Will try this.  Much appreciated. 

Hmmm, tend to agree with Casbar's comment further up this thread - sounds like you may have a dodgy earth somewhere.