Do you mean, the BEST practice for using V2L is swtiching on the vehicule?
I never use It. If you use V2L with the car switched of, then It Will use 12V battery?
Apologies if I did not make myself clear.
English is not my first language (and even worse, I do not have good vocabulary of technical terms in 华语 or in Bahasa Melayu - blame schooling that taught me a little of three languages but not a lot of any one of them!).
The issue I was trying to address was how to ensure that the low voltage battery (also known as the starter battery or 12 volt battery) of an ATTO 3 is to be kept healthy. By healthy, I mean (1) not left at a low voltage and so (2) with the lead/lead oxide plates not sulfated.
On page 94 of my ATTO 3 User Handbook, there is a sentence in articulated text (meaning a bullet point). I'll repeat that sentence here:
"In order to avoid lead-acid battery low voltage, the "Smart Charging" function will be triggered automatically when: vehicle power supply is "OFF", the power battery is allowed to discharge, and the lead-acid battery level is below a specified value."
Note the three conditions:
(1) the vehicle is OFF (meaning not ON or not STARTed);
(2) the Vehicle to Load (abbreviated as V2L or V to L or even VTOL) is used to discharge the High Voltage Battery (also known as the power battery); and
(3) the voltage of the low voltage is below some level unstated by BYD (pick a number lower than 12.7 V).
What I was trying to demonstrate by measuring the voltage across the positive and negative poles of my low voltage battery is that JUST a few minutes of using the V2L equipment (which discharges the high voltage or power battery) powering an AC electric vacuum cleaner for a few minutes was enough to lift the voltage of my low voltage battery from 12.21 V to 12.51 V. As a result, my forecast driveable kilometres dropped a little.
To repeat, nothing about turning the car ON or STARTed. If pressing the START button (or turning the car ON) was enough, then the low voltage battery would always be at a resting voltage of about 12.7 V.
I repeat, using the Vehicle to Load device, means plugging it into the Combined Charing System (CCS) socket. That socket is connected by very attractive orange colour cabling to the high voltage battery, meaning something more than 400 V on my ATTO 3.
For the tl;dr people:
leaving your car not turned "on", plugging your V2L device into the CCS charging port, and connecting to it an electric appliance such as a domestic vacuum cleaner and then using the vacuum cleaner for a few minutes to clean the car interior, means that the ATTO 3 then charges the low voltage battery from the high voltage battery.