Broken B250e

[hallcp]

Two scraps of information for you. Borrow a voltmeter and check the 12V battery voltage with the car off. It should be around 12V if not higher. If it's down to 10v or 11v then it's time to replace.

Second, the (original I presume) battery on my 2014 showed low voltage when I checked in 2019 so I replaced it. Watching voltage while turning on heat or headlights without the car fully turned on will load test the battery. Still should show 12-ish volts.

One other thought, someone on the list pointed out that when you "pre-heat" the car, perhaps by enabling it and clicking "un-lock", the 12V battery is used to produce the heat, not the big high voltage battery. Same if you turn the key one notch, but not two (mine still has a key, not a push-button). There's also that button on the dash to maintain climate control while the car is off. Same thing, it uses the 12V battery.

With the car fully awake, measuring battery voltage will only show you charging system's voltage (something over 13V, steady as a rock).

I am totally unclear if preconditioning while on charge is using the 12V or high voltage battery. I think the designer's intent was to try and avoid surprising an unwary mechanic with high-voltage when he thought the car was off.

Finally, I think almost all modern cars go completely haywire when the 12V battery finally fails. The car can show all kinds of crazy symptoms.

 

[FordAnglia]

So with that being said, would you consider replacing the 12v battery as maintenance item? If so, what interval? We haven't replaced ours yet (purchased in Sep'17 a 2015 model). I'm simply trying to prolong our use of this car, knowing how problematic they can be. We have been going strong on the new drive unit (14k miles and 18 months)

We don't have enough data to predict a B250e 12V battery fail, and replace it beforehand. To blindly replace the battery based on the date code, or vehicle miles seems wasteful to me.

A better plan would be to use a roadside service (AAA for example) to replace a defective battery. Often they have the replacement battery on their truck and also take credit card payments. Their tools can measure the health of the battery before pulling it out of the vehicle, and monitor charging performance (as an ICE car with alternator issues will result in a dead battery)

Peter,