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The Battery Of My Rav4 Goes Flat If Not Used For A Few Days.


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The alternator has to supply enough current for all the ancillaries running on the vehicle *and* it has to be able to charge the Battery while doing so. You wouldn't necessarily need a more powerful alternator for a larger Battery. If you did fit a larger alternator, chances are you'd have to replace some of the cables as well - they need to be able to carry the current and car manufacturers tend to specify the bare minimum in order to keep costs and weight down.

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Hi John.

Another way of looking at it is imagine the Battery on a car is the bath in your home and the tap filling it is your alternator. With the plug in over a given period of time the bath will fill up, so the bigger the bath the bigger the reserve capacity when filled up. When you take the plug out it's like running the ancillaries on the car, lights and heated rear windows are a heavy 'draw' hence water escaping so the alternator has to replace the electric current (Water escaping, bath plug out) faster than it is being taken away so a larger Battery will give you a greater reserve if say you are crawling in traffic, lights on, HRW on, blower on, music playing etc, etc. A small alternator will eventually charge a Battery of 'almost' any size but to upgrade from a petrol battery to a diesel one is well within the standard alternators capabilities. People that put lots of extra's on their cars, lights, sub woofers etc always end up doing battery upgrades.

Mike.

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Alternators have different amp outputs for petrol and diesel vehicles, a Rav4 Diesel engine has a much smaller rev range than it's equivalent petrol unit, so would need a higher output alternator to put enough power into the Battery, a petrol engine revs much highter so can get away with a lower amp output.

3 alternators are used in the 4.2 Rav4...... petrol, manual gearbox 90amp, petrol, auto gearbox 100amp , and diesel 130amp.

So its down to how fast the engine revs dictates the required alternator output, so to come full circle in our discussion, a petrol Rav4 alternator can easily charge up a Rav4 diesel Battery :)

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Thanks Conrod I'll bear that in mind, I'm taking RAV to my local mechanic and let him check it over, thanks again. He knows RAV very well because I always take it to him for MOT and he is good with tyres mine kept going down more than usual and he managed to fix them for me..

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  • 4 years later...

This happened to me, the AA guy said I need to ensure car is properly locked as this runs through a routine to ensure everything is switched off. Also I think it might be that the Battery in the key fob might be low and is not locking the car correctly.  

Derek

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12 minutes ago, DerekMacf said:

This happened to me, the AA guy said I need to ensure car is properly locked as this runs through a routine to ensure everything is switched off. Also I think it might be that the battery in the key fob might be low and is not locking the car correctly.  

Derek

Petrol or diesel it doesn't say in your profile? It's well known the Battery in the petrol is a 'bit small' and most owners fit the diesel size one. That includes me , just watch out for the polarity unless they are the same way round in the 4.3.

 

edit: It appears I made this comment 4 years ago earlier in this thread. Couldn't see a way to delete this post.

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