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I have a Specialized Como 2.0 (pedal assist) which I absolutely LOVE. I want to get as much exercise as possible, so I always ride it as a regular 9 speed and only hit the power button on grades or hills. (Being 71 years of age, I don't feel that I should have to struggle riding a bike anymore.) I ride mostly on Rails to Trails, so even though my power is turned on, I don't hit the "assist" button very often. My question is this: Should my battery be discharging even when I am not using it? It seems to me that if I have the power on, but never use it on a 25 mile ride, the charge should remain full. Or is it like a car where if the car is not turned on, but you leave the lights on, it'll drain the battery? I'm just confused on this point. Thanks for your help.

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This obviously depends on the motor you have, and whether you have headlights.

Headlights connected to the battery always consume some power even if your assist level is off.

However, there is also something else that could consume a bit of power. All motors have drag when not in operation. Power on but zero assist level can depending on the motor mean either "use no battery power at all" (in which case the motor drag could slow you down considerably), or "use little battery power to barely offset the drag" (in which case you have the same experience pedaling that you would if you had a non-ebike).

The specifics depends on the motor. For example, I believe my Bosch Gen3 Active Line Plus mid-drive (50 Nm) motor has a clutch so when not assisting, the motor can be entirely disengaged from the drivetrain, and thus no power usage is necessary to offset drag.

Also every electronic device will consume some minimal amount of power even if not converting that power to light or motion. So there will be at least some minimal power loss even if your motor is a clutch-type motor and if you don't have headlights. This power loss is probably so minimal compared to the energy in the big battery that it shouldn't matter.

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  • Specialized says that their mid drive motors have a freewheel mechanism.
    – Michael
    Sep 15, 2022 at 15:49
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No, assuming you are in a true "no assist" mode with lights off. The controller still shows velocity and the like but the energy for this is same as zero in comparison to the engine. I can make many kilometers with assist off that sometimes I need to do when returning down after ambitious mountain biking uphill. This has no effect on remaining range under battery power.

Maybe some models silently provide little help "to make it feel as normal bicycle" but none of my two bicycles does. Unlike in a car, brakes and steering are not energy dependent and work fine with even battery removed.

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I may misinterpret the way the question is written: what attracts my attention is that you mention "hitting the assist button", which one normally doesn't do when riding an e-bike.

It may comes from a misunderstanding on how e-bikes work. E-bikes are generally set up with assistance level that you can change with the +/- button (Bosch calls the levels Eco/Tour/Sport/Turbo, Shimano Eco/Trail/Boost, and there's an "Off" mode, where the bike is "on", but no assistance is provided), and some have a temporary assist mode, to provide additional power on request (for example, if you have to push the bike, or want to overtake/start faster).

In that case, an explanation that may be consistent with the points written in the question is that the bike is in fact not "off", but in a mode that provide assistance, which would use the power. And when you "hit the assist button", either it provides an additional boost, or the assistance you have is actually coming from the current mode.

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    Other systems do have an assist on/off button as well as power up and down
    – Chris H
    Sep 15, 2022 at 11:56
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Maybe there's just some confusion about the proprietary controls on Specialized e-bikes?

Pressing and holding the (+) button on the controls for "assist" is walk-assist mode. It is not meant as an on-demand throttle for use when riding, if that's how you're trying to use it.

How much riding assistance the bike is providing is shown in the bottom right of the display as 'OFF', 'ECO', 'TURBO' etc. and it is adjusted by clicking the (+) or (-) buttons once, not pressing and holding (+). If the 20kg+ e-bike 'feels like' a normal 9 speed it is likely on ECO ;)

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I wouldn’t be surprised if just having the electronics turned on would consume several Watts. Your eBike battery has 460Wh of energy capacity. If the electronics consume 5W (just a number which I think could be realistic) the battery would be empty after 92 hours.

For comparison, running the motor continuously at its full 250W power would empty the battery in less than two hours.

It’s possible to design an eBike in a way which allows you to turn off the motor controller etc. completely and only have the LCD display running, consuming minimal power (note how simple bike computers can run on a single coin cell battery for months or even years). But I doubt they’d go through all the hassle for a bike which is supposed to be used with the motor. I think it’s more likely they have a single voltage converter which powers all the electronics, leading to a few watts of "idle" power consumption which has very little impact on the four hours or so of runtime you’d get with using the motor moderately.

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  • It is then possible to shut down the controller completely. The lack of the speed indicator is not a big loss. But 5 W is the power of Raspberry PI while running desktop complete with web browser and word processor. For the tasks the controller does I would expect more something like 0.3 W that Arduino board uses.
    – nightrider
    Sep 15, 2022 at 15:09

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