Distance on battery reserve?

lightning

Well-known member
Apr 5, 2021
715
409
UK
For those with the Shimano battery, how many miles do you get once the display flashes red and you are limited to "eco" ?

When l first got the bike, it would run for about a minute once this happened.
Now, after around 18 charge cycles (and around 700 miles) it will run for quite some time once it starts flashing.

Tonight it happened out on the trail, as l had gone out with the battery at only around 50%

l thought "Oh crap, it's going to be a slow ride home"
But the battery hung on up two climbs and around three miles of road riding, although some of the road riding was above the assist speed.

l checked the battery when l got home and it was at 1%

Motor is E8000 and battery is a BT8035 504Wh in the down tube.
 

Gary

Old Tartan Bollocks
Author
Subscriber
Mar 29, 2018
10,496
10,692
the internet
Depends how the bike is ridden.
could last 3 easy miles or not even an 8th of a mile climbing
 
Last edited:

Gyre

Well-known member
Jan 25, 2021
629
420
Pasadena, CA
One thing that could explain what you're seeing is if the programming for the battery bar and the BMS aren't quite working together.

If the calculation for the battery bar looks at total pack output in series (i.e. where it is between 42 and 30 volts), that can give you a quick and dirty approximation of the charge remaining.

If the pack is unbalanced, the BMS has to shut down the party the moment *any* of the cells drops to ~3V or so. If the battery bar formula is using series voltage, it's implicitly assuming your pack is perfectly balanced but it never considers how close the BMS really is to turning off the taps.

While your pack was sitting in storage waiting to be delivered to you, it may have become unbalanced, so the BMS may intervene when your pack's series voltage was not particularly low (say, 32V or something like that). A few charge cycles close to 100% would give the BMS a chance to balance the pack, and then your series voltage and BMS shutoff would be more in tune with each other.

I'm not saying this is how the Shimano software actually works, but it's a hypothetical that would explain what you're seeing.
 
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