Why is my battery draining
Battery draining
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There could be several reasons for this to occur.
The battery is failing, it is not being charged correctly or there may be an excessive parasitic current draw on the battery due to a component fault somewhere.
Check the simple things first e.g. are all the lights etc turned off when the engine is turned off and the car is parked and locked, especially check that the trunk light is off. I think that the trunk light on/off switch is in the latch which means the trunk lid needs to be shut, so you may have to place a phone set up to take videos in the trunk to see if it is off or not
Use a DMM (digital multimeter) to check if the battery is being charged correctly in case of a faulty voltage regulator or alternator. To do this, safely park the car and with the transmission in Park (AT) or Neutral (MT) and the parking brake firmly applied start the engine and use the DMM to measure the voltage across the car battery terminals. It should measure between 13.8V DC - 14.5V DC. Be safety aware as the engine is running!
If the charging voltage is OK, turn off the engine and then disconnect the -ve battery lead from the battery and connect the DMM between the -ve battery terminal and the -ve battery lead and change the DMM function to DC Amps to measure the quiescent current being drawn from the battery
Normally there's 50mA-80mA of current being drawn from the battery with everything switched off. If there's more than this, you will have to remove all the fuses, one by one and check if the current drops back to normal when a fuse is removed. Remember to replace the fuse before removing the next one. If the current does drop back to the normal value when a fuse is removed, check the fuse layout diagram in the fuse box lid (or owner manual) to see what the fuse is used for.
If the quiescent current draw is within the range of normal .i.e. 50mA-80mA then perhaps the battery is failing. Get a car battery replacement service to check the condition of the battery by performing a battery discharge test.
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