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Flat battery (again) on Rav4


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My 2004 Toyota Rav4 would not start again on Christmas Eve. tried to turn over but did not manage to fire and it appears the Battery is flat.   This is an ongoing problem, I have had two new batteries in recently, one heavy duty, and my mechanic says there is nothing wrong with the alternator.  I do do shortish journeys especially in this climate but so do other people and my previous Honda never had these problems.  Any advice or shall I just get rid of it, which would be a shame as its normally such a reliable car. Thanks

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Hi Monica,

Is it petrol or diesel?

Can you describe exactly what it is doing when you try to start?

When the Battery is flat how do you start it, jump leads or Battery charger. Once it's charged/going how long does it last before it won't start again?

Have you checked you haven't left the interior light on or similar (not meant to be patronising - but it can go unnoticed)?

 

 

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Thanks for your replies.  Its a petrol car.   My mechanic usually comes and jump starts it and takes it back to the garage and charges the Battery overnight.  Its then OK for a few months.   But having let me down at Christmas, I really need to get this sorted out and no I have left nothing on, beeps if lights are not turned off and always check all 5 doors are shut properly.

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Although it is true that a cheap multimeter is all you need to get to the bottom of this you should be aware that when measuring current it is very easy to fry the meter, or at least blow its internal fuses, if it is wrongly used. Firstly you should always start with the high current setting of the meter ( usually the 10 amps range) and even then you should not under any circumstances try to start the vehicle while the meter is connected in series with the Battery and negative lead. Even switching on headlights would probably be enough to overload the meter. Only very expensive meters with inductive ( non contact) pick ups can be used to measure starter current. When you do have a reading for current draw with the vehicle switched off you can calculate how long a fully charged Battery will stay active by dividing the Battery capacity by the current. For example a 45 AmpHour Battery being drained at 50 milliamps

45/0.050 = 4500/5 = 900 hours = about 36 days

So you can see that 50 milliamps constant drain wouldn't be very healthy unless the Battery is charged every few weeks.

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So it's ok for a couple of months.

What is your usage pattern during that time eg daily journeys vs one journey a month? What sort of mileage are you doing in the month, how many hours are you driving for (just roughly)?

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My 2005 RAV4 is a second car, and only gets used once a week or fortnight, and not for long runs.  I find that the Battery will go flat in about 3 months with that sort of usage, so I use a trickle charger every six weeks or so, to prevent that.  Batteries like being kept fully charged, so will last longer of charged more frequently.  Conversely, the useful life will be appreciably shortened if subject to deep or complete discharge several times.

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Hi, You need to get your car started via jump leads or jump pack then get mechanic to check that the Battery is charging via your cars charging system with a voltmeter. You should see a flat Battery charging up in 0.1 increments. Anything less than 12.5V is considered discharged. Also check that the Battery type is correct one for your car. Turn all the lights and heating on and the charging rate should still keep up. Could be corroded Battery earth connection. Get him to check good Battery ground - you need low resistance of less than 0.3 ohms from -ve terminal to any ground bolt. Any auto electrician would be able to diagnose any of this within minutes. Definitely not worth getting rid of the car just for this!

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