How long can I leave it charging?

How long can I leave it charging?

Is it advisable to leave my HPWC in my MS while we are away on vacation for a week or two...or is it recommended to just plug it in again when we return? I think the MS recognizes when to charge and when to shut off but was just thinking that it probably doesn't make sense to pay for the amount of charge lost from sitting inactive ("vampire load") while we are gone...right? Thx for the help.

Mark K | July 30, 2013

It will consume the same amount of kWhs either way. The energy will come from the battery or the wall, so you will have paid for it in either case.

But that's a pretty small cost (3-4 kWhs / day). By the end of this year, that will go down to less than 1 kWh / day.

In general, you can't go wrong by being in the habit of leaving it plugged in at every opportunity.

nickjhowe | July 30, 2013

There was a comment in another thread from "an engineer" that if you are going away for an extended period dial the current down from 40A to 15A or so to keep the batteries topped off. Having said that the S probably wouldn't pull 40A anyway if it is just keeping the batteries topped off, and this was only one comment so can't be considered definitive instructions from TM.

Vampire load is going to be c. 10m/day depending on temperature, so if you are going away for a couple of weeks I'd definitely leave it plugged in, and in fact I'd leave it plugged in regardless. There has never been any evidence that leaving it plugged in is a bad thing, and there have been several recommendations that you should - including in the owners manual.

nickjhowe | July 30, 2013

Correction - per the TM Tech Talk referenced in this thread you should charge at 40A; do not trickle charge.

Theresa | July 30, 2013

For extended leaves my suggestion would be to dial down the total charge limit to ~ 50 -70% as from what the forums have been saying the battery longevity is best preserved in a 50-80% charged battery.

DigitalSavant | July 30, 2013

I had to leave mine for three months, so I checked in with the service center. Their response was simply, "Leave it plugged in. In fact, it's best to leave it plugged in all the time." So, I left it plugged into the NEMA 14-50 outlet in my garage and all was fine when I returned home three months later. Of course, I couldn't help but check in on it every day with the smartphone app. :-)

201w77 | July 30, 2013

Thanks everyone! Very helpful.

Jolinar | July 31, 2013

I think even owners manual says you should leave it plugged in whenever possible, especially when you do not intend to drive it anytime soon.

J.T. | July 31, 2013

If you leave the cable plugged in is the car supposed to maintain the level you set without any input from you?

mjs | July 31, 2013

I can't leave my car charging for more than about 4 hours.

As it sits in the charger, the pressure to drive it continues to build, and by about the 4th hour, I can't stand it and have to go for a drive.

Is that normal?

KOL2000 | July 31, 2013

Done this a few times for long periods including now. I set the battery to exactly 50%, leave HPWC plugged in and have noticed via the app that it charges for a few minutes every 2-3 days to offset vampire drain.

J.T. | July 31, 2013


Okay, I'll monitor it and see if it brings it back to preset level automatically. Thanks.

Brian H | July 31, 2013

Fairly wide "swings", hysteresis, around the set point. It won't hold the charge level very close to the set point, like a themostat. | July 31, 2013

I recently did a 10 day trip to Hawaii. Left the S plugged in on standard charge. My phone app told me it topped off about every three days to make up for the vampire loss.