Bosch logic for charge/discharge with swapped packs?

Gyrre

New Member
Region
USA
I have a Bosch powered bike with a piggyback frame mount extender being installed. I intend to carry either a spare frame out or a Powertube for very long days with lots of climbing.

Has Bosch published information about how the logic handles swapped batteries in piggyback configurations? I've heard that the motor normally draws from both batteries simultaneously. If I run the bike down to 10% charge and then swap out one of the two batteries, will it continue drawing from the batteries simultaneously or will it draw solely from the fresher battery until it the combined charge drops to 10% again?

Likewise, if I charge both batteries either fully or partway and swap in a near-empty battery, will it charge only the emptier battery solely until it catches up to the fuller battery? If the fuller battery is 100%, can it still "fast charge" the empty battery?
 

David Berry

Well-Known Member
Region
Australia
City
Ipswich, QLD
The motor normally draws from both batteries simultaneously.
Gyrre, I think Battery #1 is used until its reserve has dropped from 100% to 95%; then Battery #2 is used until it's down to 95%; back to Battery #1 for the next 5%… and so on.
If I run the bike down to 10% charge and then swap out one of the two batteries… will it draw solely from the fresher battery until it the combined charge drops to 10% again?
Yes, Battery #3 will be used until it has dropped to the same level (10% in your example).

These are my observations based on my Kiox's display and, on very long rides, swapping the almost depleted piggybacked PowerPack on my R&M Homage for a similar PowerPack taken off my Trek Powerfly.
 

Gyrre

New Member
Region
USA
Thanks so much for the input. I do have a followup question. My piggyback battery was finally installed. However, the charging sequence doesn't make sense. My Powertube battery started around 70% and the PowerPack frame mount battery started at 29%. I read a post on this forum from a Bosch expert that the weaker battery gets the charge until both batteries achieve the same level, then they alternate charging at 10% increments until reaching 80%, at which time perhaps they trickle or something. Unfortunately, I'm having a hard time finding the original post that said that.

Prior to charging the charge split was something more or less like 70/29 (PowerTube / PowerPack)
Some time later, it was 73/36.
A bit later after that, 75/36.
Finally, it hit 80/36.

This isn't at all what I expected to see. My understanding from that Bosch post I saw awhile back is that it would charge the low pack exclusively but instead it seems that only the mostly full pack is getting the charge. Didn't someone at Bosch explain that that's not how it's supposed to work?
 

Gyrre

New Member
Region
USA
A firmware update changed that charging sequence.
If that's true, it doesn't make sense to me: My batteries are getting *highly* unequal charging this way when they should be more or less balanced. What is the logic "supposed" to be and has any Bosch rep articulated some kind of rational explanation?

Edit: As of this morning, the charge between the two batteries is even worse, now at 89/36. That makes absolutely no sense at all. One is getting excessively charged and the other is barely one-third full.

Edit: Following up - it looks like it's taking the main battery to 91% and then charging the frame battery. That's not an ideal strategy in my book, but at least it's not taking the main to 100% before charging the frame battery.
 
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