Looks like my first ER9 set is a lemon.  After the RD gave me batt drain issues, the right brake lever also has a fault.  When pulling the brake lever, at first it travels normally, hits the wall of resistance when the caliper pistons move and brake pads press against the rotor (normal so far).  But when more force is applied, a loud clunk comes from the hinge area of the brake lever/shifter, and there is no further force generated by the hydraulics to squeeze harder on the rotor.  So essentially, the rear brake doesn't work no matter how hard I pull on the lever.  There is felt resistance at the lever, but it feels like something gave way internally of the lever and no fluid is moved from that point.  There are no fluid leaks to be seen anywhere.

So to troubleshoot, yet again I had to rob parts from my 2nd ER9 set, installed the right shifter and it totally works fine.  No more brake issues.

Contacted 80's designer again to request for a replacement and awaiting their response.  Meanwhile I'll try to dissect the lever and see what's wrong if possible.

It's definitely concerning to hear about the ER9/X RDs just dying. By any chance do you have a bar code on your RD? Joe from China Cycling said it should say the manufacturing date. Reading the first 6 digits, mine says 250123. If that's dd/mm/yy, that means I have an RD from early last year. 

I'm not sure I would take the ER9 groupset as my travel bike either. Luckily I have other mechanical bikes for travel. I'm just wondering if there's a way we can narrow down the problematic groupsets or if they're all ticking time bombs! 

I have two ER9 sets, one with the RD phantom batt drain fault that I described a few pages back.  Both have serial numbers starting with 250123.  First set was bought in Nov 2023, second in Feb 2024.  More likely that these numbers are just product codes identifying it is an ER9 RD with the following numbers the actual serial number.  Unless someone actually owns an ER9 RD that has different first six numbers.

I'm hesitating installing the 2nd ER9 set on my gravel tourer due to reliability concerns.  When riding on the road near home in relatively good conditions, its not a big deal, but in a foreign country with limited access to LTWOO ERX/ER9 parts, its a big risk unless you carry a spare ER9 RD around on your travels.  With SRAM and Shimano, almost every decent bike shop will be able to provide the needed parts in a jiffy.

Finkster. Did you have the same nick in clubsnap years ago?

Yep! 

I had a to get my shifter on my GR9 group replaced. 80 Designer store sent me another and I paid shipping. They had the typical timezone delay on responses.

Just received a reply from 80's designer on sending me a new RD and wanted US$15 for shipping. 

Is something waking your er9 from time to time?

Also check if the battery was fully charged in the first place. On some power banks the charging may stop but the batteries may not be at 100%. Always visually confirm the battery percentage in the app before unplugging the charger.

Its actually on my trainer bike so its rock steady and not moving at all.  Initially I used a power bank, but switched to a wall socket to ensure.  Yep, I confirmed the batt was full via the app.  But it just steadily depletes even when not in use.  During a 1hour zwift ride, it drops maybe 2 to 3% so its definitely not a huge drain when the derailleurs are shifted.  Another strange thing is I always have to press the RD button in order to connect to the app, even though I had just shaken the RD to wake it up 3 secs ago and the green light blinks to indicate it is awake.  My other ER9 set doesn't need the button press, just the shake to wake.  So I thought something is wonky...