HELP Checked my rear battery 13.1V is that bad
MBWorld Fanatic!
Joined: Jul 2012
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From: Canada
07 E63 + 07 CLK63CAB
So, just what is the voltage reading now with the "new" alternator installed. 14.1 or 14.2 with engine running
For trying to be frugal, you sure have poor deductive diagnostic reasoning.
Did you load test the batteries, or how about an alternator output check, just because the brushes are a certain length does not mean the unit is right. Possible shorting of the alternator when your seller removed it or if the car was involved in a crash then possible to short out the charging system at that time. Used is not always the best value when buying electrical items. They all look good, but the operation can be sketchy, as you have found.
To repeat myself, have never in my life seen any 12V battery in normal usage give 13V readings.
For trying to be frugal, you sure have poor deductive diagnostic reasoning.
Did you load test the batteries, or how about an alternator output check, just because the brushes are a certain length does not mean the unit is right. Possible shorting of the alternator when your seller removed it or if the car was involved in a crash then possible to short out the charging system at that time. Used is not always the best value when buying electrical items. They all look good, but the operation can be sketchy, as you have found.
To repeat myself, have never in my life seen any 12V battery in normal usage give 13V readings.
Thread Starter
Member
Joined: May 2011
Posts: 160
Likes: 1
From: NY
2005 E55 AMG
So, just what is the voltage reading now with the "new" alternator installed. 14.1 or 14.2 with engine running
For trying to be frugal, you sure have poor deductive diagnostic reasoning.
Did you load test the batteries, or how about an alternator output check, just because the brushes are a certain length does not mean the unit is right. Possible shorting of the alternator when your seller removed it or if the car was involved in a crash then possible to short out the charging system at that time. Used is not always the best value when buying electrical items. They all look good, but the operation can be sketchy, as you have found.
To repeat myself, have never in my life seen any 12V battery in normal usage give 13V readings.
For trying to be frugal, you sure have poor deductive diagnostic reasoning.
Did you load test the batteries, or how about an alternator output check, just because the brushes are a certain length does not mean the unit is right. Possible shorting of the alternator when your seller removed it or if the car was involved in a crash then possible to short out the charging system at that time. Used is not always the best value when buying electrical items. They all look good, but the operation can be sketchy, as you have found.
To repeat myself, have never in my life seen any 12V battery in normal usage give 13V readings.
Last edited by E55AMG05; Jan 14, 2014 at 02:50 AM.
MBWorld Fanatic!
Joined: Jul 2012
Posts: 1,556
Likes: 15
From: Canada
07 E63 + 07 CLK63CAB
Disconnect the aux battery negative connection, test voltage on the aux batt. Do not drive the car as the aux battery is there to power the brakes, but with the aux bat disconnected start the car and read the voltage, this way you are only powering the rear trunk batt. The alternator should have enough power capability to maintain 14.1V or 14.2V with the car running and the lights, radio and the AC at idle. If the aux batt is showing less than 12.5 after sitting for a while then it is time for replacement, 5 years out of a battery is good, trouble usually starts after this time frame. The power(amperage) comes from the alternator and the voltage is stabilized by the regulator, without the reg then the voltage would rise and fall according to engine RPM and at high RPMs the voltage would rise to 16-18volts which will harm the electrics of the car. Compromising and trying is expensive and wasteful of time. When in normal operation the power is distributed to recharge both batteries, if the front bat is low then possibly your trunk battery is being allowed to drain below a threshold which gives you the dash comments, because the aux bat is taking too much charge for too long.
Thread Starter
Member
Joined: May 2011
Posts: 160
Likes: 1
From: NY
2005 E55 AMG
Disconnect the aux battery negative connection, test voltage on the aux batt. Do not drive the car as the aux battery is there to power the brakes, but with the aux bat disconnected start the car and read the voltage, this way you are only powering the rear trunk batt. The alternator should have enough power capability to maintain 14.1V or 14.2V with the car running and the lights, radio and the AC at idle. If the aux batt is showing less than 12.5 after sitting for a while then it is time for replacement, 5 years out of a battery is good, trouble usually starts after this time frame. The power(amperage) comes from the alternator and the voltage is stabilized by the regulator, without the reg then the voltage would rise and fall according to engine RPM and at high RPMs the voltage would rise to 16-18volts which will harm the electrics of the car. Compromising and trying is expensive and wasteful of time. When in normal operation the power is distributed to recharge both batteries, if the front bat is low then possibly your trunk battery is being allowed to drain below a threshold which gives you the dash comments, because the aux bat is taking too much charge for too long.
Last edited by E55AMG05; Jan 15, 2014 at 12:02 AM.
MBWorld Fanatic!
Joined: Jul 2012
Posts: 1,556
Likes: 15
From: Canada
07 E63 + 07 CLK63CAB
Wow Russ, that is quite the adventure, that finger will be really painful for a while because when you put it through the pulley it twisted your finger, you might want to check to see if you broke it. Before you go out and purchase an aux battery measure the voltage of it with the car off, I believe you will see below 12.2V, with the key on depress the brake pedal and watch the voltage on the aux, it will probably dump below whatever the first voltage was.
Again sorry about the finger, fingers have many nerves in them and the pain is indescribable, try holding it up should reduce the pounding.
Again sorry about the finger, fingers have many nerves in them and the pain is indescribable, try holding it up should reduce the pounding.
Thread Starter
Member
Joined: May 2011
Posts: 160
Likes: 1
From: NY
2005 E55 AMG
Wow Russ, that is quite the adventure, that finger will be really painful for a while because when you put it through the pulley it twisted your finger, you might want to check to see if you broke it. Before you go out and purchase an aux battery measure the voltage of it with the car off, I believe you will see below 12.2V, with the key on depress the brake pedal and watch the voltage on the aux, it will probably dump below whatever the first voltage was.
Again sorry about the finger, fingers have many nerves in them and the pain is indescribable, try holding it up should reduce the pounding.
Again sorry about the finger, fingers have many nerves in them and the pain is indescribable, try holding it up should reduce the pounding.
MBWorld Fanatic!
Joined: Jul 2012
Posts: 1,556
Likes: 15
From: Canada
07 E63 + 07 CLK63CAB
Good to find that low voltage on the aux batt, now with the car running are you seeing a rise in voltage in the aux, this will show you that the charge is being sent to the AUX through the module that feeds both batteries in your car. This is just a check. But it still looks like the AUX is toast. Hope the finger is getting better.
