The battery is always running down and there is a power drain somewhere in the system when the car is turned off. I need to check the fuse box manual to know by removing one fuse at a time to see which part of the electrical system is causing the drain on the battery. I don't have the owners manual to check which fuse is for which area of the system
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Re: power drain on battery
Get a fuse tester, which looks like an icepick with a wire coming out the back. Clamp the wire to something metal to make a ground and touch the tops of the fuses which should have small metal prongs on the tops. If the handle of the tester lights up then the fuse is good and if it doesn't then the fuse is bad. Try this out and let me know.
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Jump starting a Lexus (I have one too) only gives enough power to start the car and a modest run will top up the battery. What you need to do is buy a battery charger and FULLY charge the battery. If the battery goes flat after this, there can only be three things wrong.
1.The battery needs replacing due to age or a defective cell.
2. you have a voltage drain somewhere.
3. The alternator isn't charging the battery. Is the charge light on?
I replaced the original OEM battery on my 2005 ES330 about 3 years ago.
You either have a faulty alternator or there is a constant power drain on the battery when the car is switched off as a result of a fault in the electrical system.
If i it is not charging fully as designed the only other source of power whilst you are running the car is the battery. Thus the battery will drain.
2. Slow power drain.
This will occur when the car is idle such as overnight. In this case, power is continually being delivered to a system on the car which is meant to be inactive due to a fault with the electrics. This can run the battery down so low the starter motor will not kick over when you try and start the car.
You need to get the car to a competent mechanic for tests so he can identify the cause and rectify it. For example if the old alternator is faulty and will not deliver sufficient charge to run the vehicle you will need to install a new one.
I suspect parasitic draw. All vehicles draw some power from the batteries when the car is shut off. Certain accessories such as clocks, radios remote door openers and alarms always need power. The normal power used is called parasitic draw.
It is always a very low draw so it doesn't run the battery down. If you install accessories like shortwave radios or plug things like inverters and portable refrigerators into the accessory socket and operate them too long without the engine running you can drain your batteries to the point where the engine won't start. If there is an electrical short in the vehicle or a malfunctioning accessory it could be drawing much more than its normal load causing a drain on the batteries. If you leave your door open and the inside lights stay on all night you could drain the battery down till the car won't start.
It is poss that yr battery is shot. If one of the chambers is down the rest go down fast. Get yr battery chked now. Otherwise you hv a short in the vehcile somewhere, but probably the battery is the fault.
You do not say what brand and model vehicle you have.
The rear window demisters drain a lot of power and are usually programmed to switch off automatically after about 15 or 20 minutes of use. They should also cut out fully when the vehicle's ignition is turned off and of course when you manually switch them off.
1. When you are driving and running a host of electrical units simultaneously in winter there is maximum power drainage and any shortfall in power from the alternator has to be drawn from the battery. This will be a problem if you have a weak battery that is not holding it's charge well or if the battery is not fully charged once it has been nearly or fully drained. It will also be a problem if the alternator is not producing it's optimum power while the vehicle is running.
Batteries do not respond well to being drained frequently and when they are they should always be fully charged again each time with a battery charger at the earliest opportunity. (Running them down and then expecting the vehicle's alternator to do all the battery recharging is not a sound practice).
2. It is possible the rear demister is not shutting down automatically after a period of operation as it is likely to be programmed to do in your vehicle. This is easily checked. If it is not shutting down, and the battery is needed to supplement the vehicles power supply when driving, then the battery can be run down in time.
3. If the rear demister is left active but not shutting down when your ignition is turned off your battery will quickly drain. You should check that power to the rear demister is off once the ignition is switched off (and when you switch the demister off manually). This is unlikely to be a problem but in the unlikely event that you find it is still operating then you can pull the fuse dedicated to the rear demister.
Have the alternator tested, perhaps the battery as well. Otherwise, there may be an electrical drain somewhere and that would have to be looked at by someone who knows about vehicle electrical systems. Try the battery and alternator first....
Having the fan run on for a bit after the engine has stopped is not abnormal in itself, but 20 minutes sounds excessive.
If the fan does eventually shut off, I'd consider changing the thermoswitch (this is a sensor screwed into the radiator somewhere near the bottom, with a pair of wires connected to it - to change it, you'll need to drain the cooling system).
If the fan stays on continuously until the battery is completely flat, see what happens when you unplug the wires from the thermoswitch. If this stops the fan, you need to replace the thermoswitch. If it doesn't, then you need to examine the wiring associated with the switch and the fan, looking for damaged insulation.
You have a power drain from somewhere,either an accessory or a diode in the alternator.Take the hot wire off the battery (vehicle running)and see what is still running and that will be the accessory draining power.If nothing shows up then it would likely be the diodes in the alternator have failed.
You have an electrical short somewhere in the car, and it's what is draining the battery. Put a lightbulb inline with the battery (between the battery and the negative cable). You should see it light up. Get your fusebox diagram out and remove the fuse for the radio and any security system (since power always runs through these). Then remove each fuse one by one, and watch the bulb. When you pull a fuse, if the bulb stays lit, that's not the one you want. Put it back and pull the next one. When you pull a fuse and the bulb goes out, you've found the circuit that is conducting and causing your battery drain. From there, you have to troubleshoot the circuit to find out which component is failing.