Smart System power connector

[Scuirus]

I have two bikes with Smart System. The charge state is at 70-80% for both batteries. It's now winter with snow, ice and quite cold (currently about -10 C) here so I will not be biking anymore before April/May.

What's the cheapest connector which I can use to connect to the battery to drop the charge state down to about 50%?

I will use a 75 ohm power resistor to dissipate the energy.

 

[Spiff]

Battery connector has 2 thick wires for motor current and some thin wires for data communication between motor and battery, battery output has a MOSFET Output Switch and before this switch opens to deliver current, there should be a successful comunication with the motor.

Summarizing, there is no way to discharge the battery besides a motor or the Bosch Battery Diagnostic Device, so you better put your Winter Tyres and ride it. But, 70% is a good level for storage (Recommended by Shimano, I do not know Bosch) and it will not degrade.

 

[Scuirus]

Thanks for the feedback. But I had made the cable with the power resistor and reduced the charge state of both batteries to 50% before I read your answer...

I bought these two Bosch parts

EB12100015
Bosch Adapter Dual Battery Oppsett Smart System

EB1212002S
Bosch Batterikabel 400mm Smart System

I cut the two power wires (red and black) to the second connector of the cable and soldered in some cable, a fuse holder and a 400W power resistor I had at work. And I used heat shrink tubes over all solderings.

.
You are right it's not possible to connect directly to the battery since I wasn't able to close the MOSFET switches.

But the connector can also be used in the charging port. The charging port and the motor are connected to the battery in parallel. So I could dissipate the energy trough the charging port. The only disadvantage was that the ebike switches off after about 10 minutes of inactivity. I have the bike inside my apartment so it was not that much hassle. By pushing a button on the controller I got 10 minutes extra. But I had to switch on the ebike a lot of times to reduce the charge state of two batteries by 20% each. A 7.5 or 10 ohm power resistor would have been more suited than the 75 ohm I had for the task. Maybe I will modify the cable before next winter.

I'm an electrical engineer designing products with 18650 li-ion cells. We have specified 40-60% storage charge state for our products, so I want to be in the middle of this interval for my eBike batteries.

 

[Spiff]

Nice Work!!!!.

I am Bosch User since last Black Friday (and I am also EE), and I am still finding and reading Bosch tech info, and in a Facebook Group about eBike Extenders it was explained that the reason why it is so difficult to add a no brand battery extender to a Gen4 Smart System, it is because battery has an internal shunt resistor to sense current provided by the battery to the motor, and another one inside the motor, and during battery to motor data handshaking both values are compared and if they do not match then motor suspects of an unathorized battery extender, throws an error code and stops motor operation.

I understood that this theory would also apply to an external resistor in battery charge connector but either this theory is false or it does not apply to a resistor.

 

[Scuirus]

I quite sure it's inactivity, no pedaling and no operation of the controller, which is shutting down the system with the resistor connected. If it had been differences in current in the battery and motor operating the controller wouldn't have given about 10 minutes of additional operation. How it is when biking I have no idea about.

I'm running Tour+ and eMTB mode so I've never been even close to discharge the battery completely. And since I have two bikes with 750 Wh batteries I will just bring the second battery if I go for a two day trip.