Battery

[French02chris]

Hello all...
First, my car is 1993 W124 400E (324k miles)

Every morning for the past few months, my battery voltage shows 12.2 in the morning.
It showed less during one morning in Florida when it was 25 degrees (fahrenheit) around Christmas time (like 11.8 if I remember correctly)

Since that time, I got 2 misfires when starting & a weird thing when the rpm would not go down... After restart of the car right away, everything was fine..

Question : should I replace my battery now??

Thank you
Christophe

 

[nocfn]

It is my novice opinion but experience here in Houston, heat kills batteries faster than cold. (grew up 19 years in Cleveland, Ohio).

if you have a 30 to 36 month-old battery, I would have it tested for dead cells. If your alternator is equally as old, good chance the brushes are shot on the voltage regulator. It is a coin flip, but the alternator removal is tedious so I put in a rebuilt one and my VR was bad as well on the 94 OE. Test that battery and the alternator before you replace any of them.

 

[French02chris]

It is my novice opinion but experience here in Houston, heat kills batteries faster than cold. (grew up 19 years in Cleveland, Ohio).

if you have a 30 to 36 month-old battery, I would have it tested for dead cells. If your alternator is equally as old, good chance the brushes are shot on the voltage regulator. It is a coin flip, but the alternator removal is tedious so I put in a rebuilt one and my VR was bad as well on the 94 OE. Test that battery and the alternator before you replace any of them.

Alternator is only a couple of years old.
The old one died 2 years ago

 

[gsxr]

You need to check voltage when running to see if the alternator is charging properly.

The battery can be load-tested to verify condition, but MUST be fully charged prior to load testing.

Replacing a good battery in a car with faulty charging system will be a waste of money.

 

[French02chris]

You need to check voltage when running to see if the alternator is charging properly.

The battery can be load-tested to verify condition, but MUST be fully charged prior to load testing.

Replacing a good battery in a car with faulty charging system will be a waste of money.

The voltage when running is between 14 and 14.1.
After a run, battery is 12.6..however, it is 12.2 in the morning.. Or after a couple of hours after a long drive

 

[gerryvz]

I don't think you need to replace it. In my opinion anything above 12 volts after the car has been at rest is fine. Have it tested (or get a battery health tester yourself) and check it out for a dead or weak cell, as mentioned. A health tester will tell you right away if the battery should be replaced or not.

It sounds like your charging system is fine, and again anything above 12V is going to be fine, as long as there aren't any dead cells.

The idle RPM of the car will be elevated for a bit after a cold start, while the coolant and engine come up to temp per inputs from the coolant temp sensor, O2 sensor, etc. That is 100% normal. It would be a problem if the car didn't, after a couple of minutes of running after a cold start in cold ambient temp, settle down to a proper ~600-650 (or whatever the official spec is) RPM idle speed.

 

[gsxr]

The voltage when running is between 14 and 14.1.
After a run, battery is 12.6..however, it is 12.2 in the morning.. Or after a couple of hours after a long drive

Sounds like you may have an electrical drain, if so, you need to isolate the offending circuit/component and fix it, or you'll end up with the same issue with a new battery.

With engine running, voltage should be around 14.0v, ±0.2 (approximately).
Immediately after the engine is shut off, voltage will likely be 13+ and gradually drop below 13.
After sitting overnight voltage should be stabilized at 12.6v.
If it's 12.2v after sitting overnight, something may be draining the battery, but a load test will verify if the battery is good or not.

I'm assuming your volt meter is accurate, btw.

 

[French02chris]

Update...
Put a new battery...
The last 2 mornings was still at 12.6v, while the older one was 12.2v in the morning.. Plus it starts easier now

Old battery was 3 years old (found the receipt)