[samoual]

Hi there i'm having different issues with my X3 but in simple words...

Is it normal that the alternator is charging at 15.3V?

The battery was reading 11.7V at 30F (outside cold temperature), so I decided to change it for a new battery which read 12.6C at 30F.

Then when I started the car as it did with the old battery the alternator is charging at 15.3V

This can't be normal....

The car has now 100 000 miles.

Thank you.

[HighlandPete]

Have you registered the new battery to the vehicle?

[e30lover318i]

Load test the battery at a local Autozone or parts store. Battery needs to be load tested with AGM setting

[Bdavi011]

+1 on registering the battery with the car. The DME is probably using the old data on the previous worn battery and using it on the new battery. I do not recommend running the car until you have done so or else your new battery will go bad or worse.

[samoual]

I changed the battery for a 90Ah lead acid, registered and it'S now charging at 14.95 to 15.05 volts when cold.

What do you guys think? Should I change the alternator?

[pungo]

Originally Posted by samoual

I changed the battery for a 90Ah lead acid, registered and it'S now charging at 14.95 to 15.05 volts when cold.

What do you guys think? Should I change the alternator?

Since you changed the battery chemistry and you never said you coded the vehicle to the new battery type and or capacity, who knows what the alternator is going to do. I recommend you take it to a professional that can properly set the correct battery type(flooded vs agm) & capacity, then register it and then check the charging system for proper operation.

[383vett]

Your car originally had a AGM battery. I'd go back to that type and register it.

[e30lover318i]

Posting info from a previous post on this forum

1. Normal charging at around 13.6 to 14.0 volts for the first few miles after starting.

2. After a few miles, the charging voltage drops to 13.2 or 13.3 during steady cruising, indicating a low load, low (trickle charge) situation.

3. At throttle lift off or brake application, the voltage shoots up to 14.8 volts, indicating a maximum charge rate and high alternator load. This continues as the car slows down and the transmission downshifts through each gear to keep the engine speed above 1200 rpm minimum so that the alternator can develop maximum output.

4. Once the car is almost stopped, the torque converter unlocks and the engine drops to a low idle. The charge voltage then drops back to 13.2 indicating a light load on the engine.

[e30lover318i]

Blindly replacing parts is never a good idea. Newer bmws have a BCM “battery control module”. The alternator is being commanded by the BCM on how to charge, this is not a normal charge system with just a voltage regulator. There are a multitude of things that come into play on this new system so get a scanner/software to properly diag before you start playing musical parts.