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Prius Gen3 12V Battery Trickle-Charging

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I'll be leaving the car in the garage for a long weekend, and think it would be an ideal opportunity to give the 12v Battery a good charge while we are away. Seems every other thread on here is about the 12V Battery so why not? Lol.

I can see the Battery in the boot underneath the various covers, is there any problems with trickle charging (I'm thinking less than 1A) with the Battery in situ? If I have to go through the hassle of removing the Battery, then I'll lose all the settings - in which case I may just leave it instead, it'll be less hassle!

Any opinions, tips?



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I get your drift, but I've done this on many other cars, so pretty confident of what I'm doing, just wondered whether there was a good reason not to with a hybrid. :-)

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So called 'intelligent' chargers like the CTEK3600 can, according to the manufacturer anyway, be left connected for months. Personally I've never left it connected for more than a couple of days but my Prius has never had any issues with having its Battery charged while connected.

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Thanks, made my mind up, I think I'll be doing it. If my Prius explodes over the weekend (16-17th Feb) I'll let you know :-)

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Why don't you decoke the engine whilst you're at it? Hell it doesn't need doing but I suppose you can't be too careful eh?

My Prius is at the 70,000 mile mark where 12v's are meant to start showing signs of failure. The car has been sat for over a week and starts first time, every time. I can't understand charging 12volts unless you're going away for more than a couple weeks. If a 12v needs to be charged outside of the car it's dead and needs replacing.

But I guess some people like tinkering for the sake of it and good luck to 'em.

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The 12 volt Battery in our gen 2 is about 4 years old and I suspected that leaving the car parked in a cold airport car park for 15 days might be a bit too much for the weedy Battery to sustain. I therefore bought myself a combined battery/ compressor /lamp prior to travelling and left it in the car in the knowledge that if the Battery gave up while I was away, I could simply connect up the booster on my return.

My guess was correct. The car wouldnt unlock from the keyfob and all the 12 volt systems failed to operate on my return to the uk. The process of popping the bonnet, connecting the booster to the underbonnet terminals and starting the car took all of 5 minutes of somewhat unhurried activity and we were away with just the car clock to reset and the radio to retune.

The 12 volt Battery is still perfectly adequate for day to day operation and I dont expect it to present any problems at all until the next time I leave the car parked out of doors in low temperature for a prolonged period of time. The booster Battery will remain in the car just in case.

Our other car, a CT200, was locked away in our garage at home for the duration and its Battery stood up to the period of inactivity due to the temperature in the garage being a couple of degrees higher and the age of the equally weedy Battery being a couple of years less than our prius Battery.

Since Toyota based hybrids use the traction Battery to start the engine, the 12 volt batterythey use does not need to be heavy duty since it doesnt have the heavy load of starting the engine placed upon it, As a consequence of the 12 volt Battery being lightly loaded with a few lamps and electronics, they are likely to quietly degrade to a state whereby they become next to useless prior to causing problems, whereas your diesel car Battery carries a heavy starting load and actually carries quite a lot of otherwise useful power when it reaches the point that it wont turn the starter motor hence the reason why it is often possible to leave the hazzard flashers on a diesel with a 'flat' Battery.

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