Left the dome light on in 2008 Toyota Highlander for 48 hours. Came back to completely dead battery. Called AAA to come jump the car and the guy said it had been depleted from 12.6 all the way down to 3 volts, and that I should drive it for 45-60 minutes. To be on the safe side I drove it for two hours. After that I left and the car has now been sitting there for 3 days. I’m about to go on a 3 hour road trip, but I read some things stating that the alternator is not designed to recharge a depleted battery and it could damage the alternator. The battery is almost brand new (installed 2 months ago).
Is there any risk of messing up the alternator or should I just go ahead and drive the 3 hours? Will this restore the battery to full charge? Should I postpone the road trip and go to a shop and have them charge up the battery, or is this not necessary?
Or at the very least, access to an exterior power outlet?
If so, you could charge it yourself
There are many inexpensive chargers on the market which will not overcharge. They will switch to “maintain” mode when the charger detects the battery has reached 100%
You could spend far less than $100 for many of these devices, and it may not be the last time you need it.
yup . . . the alternator is designed to work with a functional battery, not revive a discharged one
I don’t have a garage or a power outlet so I’d have to go and have a shop do it. How likely is it that the alternator was damaged in the driving I did right after the jump start? AAA said that is what I should do so I did not suspect it might cause a problem.
Since you already drove the vehicle for two hours it is too late. If the charging system warning light illuminates (battery symbol) you will know the alternator is failing but there is only a small chance for that to occur. You could charge the battery now but it probably has at least a 75% charge in it now.
Okay that is helpful, thanks. Just to clarify, I can’t do any more damage through additional driving and the battery will definitely charge to full in the course of the 3 hour road trip?
During the first 30 minutes of operation after the jump start a battery can draw a lot of current, as much as 80 amps, this can overheat the alternator. At this point the battery is probably drawing less that 20 amps until it is fully charged, close to normal operation.