Is my controller 'bad'? Severe loss of power at low SoC?

[bob2.0]

Thanks for the links, I'll consider them.

But I wouldn't expect to see connectors if it was waterproof. I have doubts on the weather robustness of those.

I don't like the idea of live 72V lines being added. If they can power a readout then they can't be fed with protection resistors (else it'd change the reading).

There are too many lines at the front of the bike that remain live already (IMHO). I did not want to add yet more.

What I wanted to do was to make a plug that fits between the harness plugs of the alarm, under the seat. It'd just be a plug-in piece (I have that connector type) and I would string a 300k Ohm and 15k Ohm [the only standard resistors to make the right ratio] across the 72V to make a 1:20 (per cell) voltage, to be read by a 12V powered off the number plate light. Those 3 wires can then be safely routed to a 12V powered readout at the front.

That was my plan. I just needed a waterproof 12V powered 3 wire.

Can I please ask this to check something; in this system, is the 'negative' voltage of the 12V and 72V common? Are those already connected, or are they floating wrt each other?

I'm trying to minimise any 'further' 72V risks.

[jeff-jordan]

...
Can I please ask this to check something; in this system, is the 'negative' voltage of the 12V and 72V common? Are those already connected, or are they floating wrt each other?
...

The 12 V and 72 V circuits share the same common negative terminal—due to the DC/DC converter (with a common negative).
Please note, however: The motorcycle chassis is not connected to the common negative terminal (and should not be).