Battery Isolators - Charge or Drain isolation?

[dom14]

Sorry, but have to disagree with an sort of useful prioritising by a VSR...
When the engine is running the VSR can only 'see' the Alternator output voltage.

The Alternator reg is now in a voltage regulated current limited state IE it will continue to increase current to try and maintain voltage.
Most vehicles have an Alternator that will easily supply sufficient voltage at idle to tip the VSR when no other major loads are present (Headlamps etc)

Unless the Cranker is discharged so extensively that the charge acceptance rate is high enough to drag the Regulated Voltage Output below the cut out voltage of the VSR then the VSR will happily parallel the batteries.

I have significant parasitic drain on my Cranker and the SOC will often get down to 70 ish percent and the Alternator Voltage and therefore the Redarc will pull in within a minute or two of starting.

Hey Evil Twin,
You wanna fix that parasitic drain asap. I reckon a cranker getting down to 70% can reduce it's life span a fair bit.
Thanx for the clear explanation above.