Can leaving the door open run down the battery and am I going to recover from 5.5v

A 12 volt battery in back that is down to 5.5 volts, though, will drink up considerable current from your jump source, until it is up to a more reasonable voltage.

 

That might be true in most cases but not all.

If/when the onboard battery is REALLY low, it can drag down the jump source voltage too, resulting in a "system" voltage that still is low.
That likely IS the case when the battery initially reads 5.5 volts.

 

I'd pull it and parallel charge it.

 

In the 3rd gen Owner's Manual the recommend to delay start up for 5 minutes after connection to the assisting vehicle, and to have it running at elevated rpm for that time:



That said, I think it doesn't matter that much.

Haven't done that in the past, but sounds like a good idea: gives the dead battery more of a chance. I'm going to start doing that.

 

What exactly doesn't matter that much ?
Having a jump source of sufficient capacity connected a sufficient amount of time absolutely does matter.
Fact, not random opinion.

 

I guess I just threw that in, cus I've never waited 5 minutes, say after connecting my jump pack. But fair enough, likely a good idea: give the knackered battery more of a chance.

 

Toyota and I both thank you for your concurrence.
(Sorry, couldn't resist.)

 

Manual says “increase the speed of the second vehicle” so that means driving down the road side by side with jumper cables on both batteries and have the second car accelerate? I hate to be the lawyer for Toyota on thAt if a road accident like that was the result.

 

My screen grab says increase engine speed, c'mon...