When you get the RAV started, push on the accelerator to get the ICE to turn on. You can also turn on the heat to make sure it stays on. Once that is on, you should be able to disconnect it and it stay running. The next time you turn it off though, it wont start again. 4v is SUPER low, so make sure once you get it running, the next stop is to get a new battery.

 

What model year? Do you know why it discharged to that low?

 

I don't know anything about Maintenance Mode, however I stumbled upon it for an oil change recently.
I had a heck of a time getting the motor to rev, it would simply produce a MID warning "accelerator pedal pressed". Precisely! because I wanted it pressed to rev the motor but it failed to do so, it just kept switching to battery mode.

Look up what Maintenance Mode is for and if this is a good use for it, enable it and try to rev if you can't get it to rev otherwise.

 

Any idea where maintenance mode is documented? Not in my 2019 owner's manual.

 

If you’re only reading 4V, that’s not enough to keep the car’s computers running in conjunction with the DC-DC converter. Your battery is severely damaged. You’ll need to swap it out to get it going again.

 

So no response as to case of battery voltage. DCM? Something left on? After market accessory?

Disconnect the battery, charge it just to get it started and address the real cause would be what I'd consider.

 

Just as suspected -it allows the vehicle to be started and keep ICE on the whole time.
Next time I change oil I'll have to remember it (but I'll dig deeper first) so I can keep the motor running while to keep it warm prior to a change.

For the oil change I drove onto ramps and I was sort of concerned the ICE would come in while driving up launching me into my kitchen!

Google Search

www.google.com

 

NMD Thanks for the link.