Battery dead after sitting for four or five days

I have a 2005 Toyota Prius with almost 50K miles on it. I really like the cars performance and mileage but there is one thing that I have encountered concerns me.

When the car is parked for four or five days the battery is drained of power and the car will not start. The dealer’s solution was that I disconnect the battery when going away. The battery is hidden away in the rear of the car so this didn’t sound cool. Later they said to deactivate the Smart Function of the car and it would isolate the 4 microprocessors. I did that and it was alright for 4 days but not for 8 days.

Is this “normal” for a Prius? Given the attention to detail Toyota has put in, it seems that this may not be normal.

Comments please.

Thanks Carl

Carl, That Doesn’t Sound Right. People Have Complained About Headlights, Gas Tank Bladders, Tire Wear, And Poor Mileage On This Site, But I Haven’t Seen This One.

I’d call a couple of other Toyota dealers and ask them what you’ve asked here. I’m sure that if this was normal for a Prius, it would be a common question here.


Carl, A Search Here Did Turn Up Some Discussions. Try Clicking These Links Or Use The “Search” Feature.


If it’s the orignal battery, you might be reaching it’s reserve capacity lifetime.

That’s the amount of time where a battery is kept alive even though it’s not being recharged. Most people only look at the Cold Cranking Amps of battery to measure it’s importance. When the reserve capacity is more important if the battery is used heavily without recharge, or if the the battery sits for an extended period of time without rechaage.

In a nutshell, if that’s the original battery, it’s time for a new one.


I first had the problem before the warrentee expired and they charged the battery and pronounced it “fixed”. It happened next after the warrentee expired and I was on the hook for a new battery. Since then it has happened several times.


Does it have an alarm system or remote starter? Both can be battery drainers…

Check to see if your “power plug” (cigarette lighter receptical) is hot all the time, even with the key off. Most are… If it has a direct connection to the battery, you can plug a trickle charger into it, and maintain the battery when the car sits unused. This saves accessing the battery to connect the charger.

You could force the issue by having someone run a “Parasitic Load Test” on the battery. This will find whatever is draining it…