focus battery replacement

[XW 393]

G'day, I think the battery on my 2015 lz titanium is dying.When I replace it does the BMS have to be reset by a dealer or does it work it out on it's own?.

[marg99]

the crafty people keep the current alive by using battery stater cables on the car all the time so there remains a current This used to be important when ford had codes on its radios and you lost the code.

[stefcio007]

On the LW at least you need to reset the BMS, I assume it would be the same for LZ.

Someone on here could confirm if you can do it yourself using ForScan, that's what I used to perform the reset on my LW.

[CatonaPC©]

I have heard someone had disconnected and reconnected their LZ Ford Focus battery without any issues, but didn't mention any thing about a BMS. I've never heard of this, so if anyone can explain why you would need to reset anything, that would be great.

As an aside, the battery on my 2015 LZ had started to have issues also. I've had to put it in charge a few times. I traded it in before I needed to change the battery, but, although 4 years from a battery before it starts to have issues is a reasonable life-span, I wonder if the stop/start feature would be a contributing factor for the battery's demise.

[GTLEGEND]

A lesson on Battery Monitoring Sensor (BMS).

BMS is utilised by vehicles that are equipped with Smart Regenerative Charging (SRC) or Start/Stop system because these systems require data of the battery State of Charge (SoC) and State of Health (SoH). BMS is the sensor utilised to provide this data.

BMS reset should only be done when a battery is replaced and at no other time. The reset needs to be done via a diagnostic tool.

Any external electrical earths must not be connected to the battery earth post/terminal directly but at another earth point like the battery earth lead point on the chassis etc. Also the BMS pole clamp should not be removed unless the battery is being replaced, earth isolation should be by disconnecting the earth lead chassis eyelet. This is to prevent BMS data inaccuracy.

Connector to BMS is made up of two wires, one for LIN data bus, the other a 12V battery feed to provide power to the BMS. If the BMS needs to be removed the connector is to be disconnected first and connected last after the battery or connector refitted to the battery.

The BMS monitors voltage, current and temp of the battery to calculate the SoC and SoH. To function with accuracy, the BMS recalibrates itself at regular intervals. Recalibration occurs during a rest period when the battery quiescent current is less than 100mA for at least 3 hours. The longer the rest period, the better the accuracy. Recalibration must take place within every 7 days or the SoC cannot be guaranteed. This will result in the Start/Stop and SCR system being deactivated. These systems will also be disabled if the sensor detects the battery is reaching its end of life, low state of charge or health.

The BMS is unable to detect what type or size battery is built into the vehicle, so battery replacement should be one of the same size and type as that fitted from factory.

The BMS is also unable to detect the difference between replacement of an old battery with a new one, so a BMS reset is required to clear any accumulated battery aging data as it does not do it automatically. Failure to reset the BMS after replacing a battery can result in BMS estimating incorrect parameters and disabling the SRC and the Start/Stop system.

A BMS reset how ever does not reset the SoC level, only the accumulated aging data. To reset the SoC is done by disconnecting the power to the BMS and reconnecting it (known as Power-on-reset).

When charging a battery on car, you must not connect to the battery negative post but to the designated earth point. By charging directly to the negative post creates a blind charge because the BMS is unable to see the charge entering the battery. If the BMS does not see current flowing in or out of battery, it cannot correctly calculate an accurate SoC.

If the battery is charged out of the car, when the battery is refitted the BMS will go through a power on initialisation process for a few seconds to establish a quick and rough SoC estimate. it will take a minimum of 3 hours of rest as advised above for the BMS to re-monitor the battery charge level to a higher level of accuracy.

Also when reconnecting a BMS make sure there are no high discharge loads on the battery such as having the headlights on. High loads will cause a voltage dip at the battery which can result in the BMS reporting a very low SoC. Start/Stop and SRC may be deactivated until the rest period described above is seen.

Never reconnect the BMS when a battery is charging as it will also cause inaccurate BMS data.

[XW 393]

Thanks for the lesson. Life was so much easier when cranking up the old XY

[GTLEGEND]

Originally Posted by XW 393

Thanks for the lesson. Life was so much easier when cranking up the old XY

Yes and all you would need was a hammer to tap the starter solenoid when it got stuck and the battery would give you warning by slow crank when it was getting old in the tooth...

[frankie86]

I have changed the battery in my wifes lz titanium, swapped straight over didn't have to do a thing

[GTLEGEND]

Originally Posted by frankie86

I have changed the battery in my wifes lz titanium, swapped straight over didn't have to do a thing

You would not notice anything its just the data now going from the VMS will be an average over the original and the new battery, not just the data from a new battery as the system cannot tell a new battery has been replaced.

[CatonaPC©]

Originally Posted by GTLEGEND

A lesson on Battery Monitoring Sensor (BMS).

Thank you GTLEGEND! Now I know why the Ford service guy told me to attach the negative clamp from the battery charger to the negative post on the chassis.