Mastermind TCU battery issues


May 26, 2020
having an issue with what i think is the internal battery in the mastermind TCU (gen 3 levo - TCU2 - non replaceable battery) and after a bit of a logic check / advice

went to go for a ride tonight and bike won't turn on and TCU is completely dead. the main battery for the bike is fully charged, charged it fully 3 days ago after a ride and when i connect the charger the 4 little green LED's show it as charged. cleaned the contacts to the battery connector and no joy, so figure it must be the battery in the TCU. have removed TCU and put it on charge and now you can turn the TCU on (but obviously shows no bike battery error).

hopefully charging the TCU will get it all working again, however this is where my query comes in - my understanding is that the mastermind TCU should charge off the main bike battery while riding / in use, i was out for a ride 3 days ago for c 2.5 hours riding time, so how has the TCU battery gone flat? last ride prior to that was a couple of weeks ago again for c 2..5 hours riding time. this suggests to me that there an issue somewhere with either the TCU battery not charging when bike is in use or the TCU battery is flatting far too quickly when not in use dormant surely it should be able to survive a week or two without being charged?

any thoughts, advice or similar experience?


E*POWAH Elite World Champion
May 16, 2019
The Bosch Smart System also uses a rechargeable lithium battery in the LED Remote and some have experienced similar problems as you describe. There are 2 possible scenarios. If your bike is fairly new, the Mastermind battery may have been at a low state of charge from new and charging it directly via the USB port may wake it up fully and you will be OK from now on. The second scenario is that the battery is is not reliably getting a charge from the bikes main battery in which case only getting the TCU/Mastermind replaced wil fix the issue.
The rechargeable batteries in both the Mastermind and the Bosch Smart LED Remote, include a charge control circuit using a thermistor. If a thermistor becomes faulty its operation becomes chaotic............I suspect that component as far as the Bosch Smart System is concerned................maybe also the case with the Mastermind battery.

I would not mind betting they are the same 3.7v ( nominal) 4.2v charge, battery.

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