BMW R1200RT/R1250RT Forum

The bike, 2020 1250RT, has a lithium-ion battery less than one year old.

I changed out my exhaust system a couple weeks ago, which requires disconnecting/connecting O2 sensors.

Since, I have had the bike out twice for a couple hours each with no problems at all.

Day before yesterday, tried to start the bike and nothing. Nothing lit up, gauges, lights, nothing. Check the battery and it showed .4 volts.

Pulled the battery, hooked up the charger. Let it sit overnight. Charged back up to 12.5.

Installed the battery. Pushed the "on" button and everything lit as usual. Brought up the voltmeter in the dashboard. Battery read 12.4 volts. Hit the start button, dash went dark. Pushed the "on" button again and watched the voltmeter go down from about 10v to 4v and dash went dark again.

Made no changes to the bike other than the exhaust.

Any ideas as to where I should start looking for the problem?

12.5 volts seems very low for a lithium ion battery. I would start with the battery. Here is Shorai’s charge vs voltage chart.

Sounds like the battery is knackered

Many li-ion batteries have a built-in battery management system (BMS) to prevent over charging/discharging. The BMS can tell you if there is an issue with the battery. I would track down the manual for the battery and look for clues there.