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[Crissa]

I have noticed the more I ride in a temperature range, the more correct the SOC is and the more that's available at the bottom.

I think the bike tries its best to leave somee down there, it just doesn't always know where the cells have lost their plasticity without practice.  And cells might need that conditioning to get the most out of them)

-Crissa

[victor6.7y]

I really like the idea of a backup that I can switch on when I really need it 

I have a Zero S 14.4kWh from 2019. When trying to drive the battery to its last drop, I noticed that I was able to drive about 20km, at 30km/h when the gauge first showed 0%.
Since I have it, I’m assuming everyone has it? This sounds like a software update giving you a "limp home" battery.



I don't think a carriable limp home battery is really doable.
Let us first determine the amount of power that we need to limp home;
-   Our system works from 96v – 116v with a average of 102v. This means that we would need a “limp home” battery setup that has the same voltage.
-   Driving 30km/h will use about 20Wh/km? (just a guess) which is about 20/102 = 0.19Ah/km.
-   If we want to drive 20 km, we need 0.19*20 = 3.9Ah storage. (let’s say, 4 to 5Ah)
Actually, this does not seem impossible.

We need about 14 of the following batteries, placed in series. Then we can travel about 26km


* Take note, we would need to connect this to the motor controller and ensure that we don't kill the original battery and stuff. (this is the disclaimer to only do this when you know what you are doing)

[Auriga]

I think this would be very difficult to setup without much lower level firmware  access to the bike.

Connecting a full battery made of those to the bike's aux port with a depleted battery would cause a massive inrush current into the depleted main battery, most likely far more than the discharge rating of the small battery. Causing fire. battery damage, or worse,

The only way to do this is to have the original battery's contactor open. Trouble there is that the MBB and BMS communicate, and the bike will know the battery contactor is open and prevent the bike from running. Current consumption and other data is also passed to the MBB.  So you'd have to create a BMS that fools the MBB into thinking everything's fine.

To me, you're describing a smaller powertank, and Zero specifically only allows those to both connect if they are both almost equivalent voltage, due to this risk. The newer FST platform bikes and SR bikes will run on the powertank alone for a limited range and power though.

So to do this safely, you'd need to build the battery pack, spoof a BMS, and either only connect it with the main battery contactor open or add a contactor.

Or hope Zero decides to build something like that as an accessory

[flynnstig82r]

I had envisioned a much simpler solution than that, with no intention of running the bike's motor off the backup battery or connecting it directly to the main battery. I just want something I can hook up to a charger (probably a DigiNow SC since those can accept DC input) and feed it 32A @ 116 vdc until the main battery has the extra mile or two I need to make it to a charger. 28 Molicell 45A 21700 cells in series should do the trick.

[Auriga]

Ah yeah, much more doable.  The onboard charger or a diginow will probably take dc in. In your case the tricky part might be getting a consistent voltage across the battery pack discharge curve.

[T.S. Zarathustra]

I had envisioned a much simpler solution than that, with no intention of running the bike's motor off the backup battery or connecting it directly to the main battery. I just want something I can hook up to a charger (probably a DigiNow SC since those can accept DC input) and feed it 32A @ 116 vdc until the main battery has the extra mile or two I need to make it to a charger. 28 Molicell 45A 21700 cells in series should do the trick.

I don't believe the bike BMS will allow you to charge and ride at the same time. That means (unless you want to be parked on the shoulder while adding your limp-home-charge) you will need to spend some time in a parking lot, so you might as well spend it next to a proper charger. .
 

I think this would be very difficult to setup without much lower level firmware  access to the bike.

Connecting a full battery made of those to the bike's aux port with a depleted battery would cause a massive inrush current into the depleted main battery, most likely far more than the discharge rating of the small battery. Causing fire. battery damage, or worse,

The only way to do this is to have the original battery's contactor open. Trouble there is that the MBB and BMS communicate, and the bike will know the battery contactor is open and prevent the bike from running. Current consumption and other data is also passed to the MBB.  So you'd have to create a BMS that fools the MBB into thinking everything's fine.

To me, you're describing a smaller powertank, and Zero specifically only allows those to both connect if they are both almost equivalent voltage, due to this risk. The newer FST platform bikes and SR bikes will run on the powertank alone for a limited range and power though.

So to do this safely, you'd need to build the battery pack, spoof a BMS, and either only connect it with the main battery contactor open or add a contactor.

Or hope Zero decides to build something like that as an accessory

The inrush of current can be limited with a simple circuit. Charging resistance of a battery (even when nearly empty ) is quite high so current limitation might not be needed. If I remember correctly, charging resistance has already started to increase considerably when state of charge drops below the last 25%. The real numbers are dependent on the actual battery chemistry though.
In short, I don't see a way to add a usable reserve battery without voiding the warranty.
I think Zero would be wise to add an 10% "reserve", maybe as an selectable option. The dash might flash "You are now on reserve energy, head directly to the nearest charging point.". I believe it would have many benefits. Reduce range anxiety without reducing real range.

[flynnstig82r]

I had envisioned a much simpler solution than that, with no intention of running the bike's motor off the backup battery or connecting it directly to the main battery. I just want something I can hook up to a charger (probably a DigiNow SC since those can accept DC input) and feed it 32A @ 116 vdc until the main battery has the extra mile or two I need to make it to a charger. 28 Molicell 45A 21700 cells in series should do the trick.

I don't believe the bike BMS will allow you to charge and ride at the same time. That means (unless you want to be parked on the shoulder while adding your limp-home-charge) you will need to spend some time in a parking lot, so you might as well spend it next to a proper charger. .
 

OK, good to know! Still, if worst comes to worst I’d rather spend an hour on the side of the road charging from a bailout battery than four hours waiting for a $125 tow truck. In these scenarios, I already tried to make it to a proper charger and failed.

[valnar]

Do you have any friends/family who could simply bring you a small generator and then charge your battery for a few minutes that way?  I mean, how often do you plan on tempting fate by driving to 0% ?

There is also this company if you live in CA.
https://www.greencarreports.com/news/1128138_sparkcharge-mobile-charging-will-get-tested-by-roadside-assistance-in-sf-and-la