I know how to do it on a Mk 8 and that it needs to be carried out after a battery change.  My question is are there aby other times that this should be carried out? If so when should this be done. I ask this as I monitor my battery voltage on my mobile via a tracker device which also shows battery voltage. I will add here that the tracker voltage is within 0.01 volt of voltage measured with a volt meter. Now when I do a 200 mile journey my battery within 15 ins of  shutdown shows 12.32 volts. check again after 1 to 1.5 hours it shows 12.54 volts. So if ever necessary when should I do a BMS reset, as soon as I stop or wait 1 to !.5 hours. It might seem a stupid question to all you electrical experts out there but having been a mechanical engineer for 36 years in the Air force my electrical knowledge of cars is limited.

The BMS should only be reset if the car battery has been replaced. Even if the car battery has been charged off the vehicle or it has been charged on the vehicle but with the negative lead incorrectly connected to the battery, instead of correctly connected to the chassis earth point.

If the battery has in some way been charged or discharged without the BMS knowing, it will within 48 hours of normal use correct itself.

Resetting the BMS for any other reason than fitting a new battery should be avoided as this will erase the battery in service, 'Days elapsed counter'

50 minutes ago, jsk said:

Now when I do a 200 mile journey my battery within 15 ins of  shutdown shows 12.32 volts. check again after 1 to 1.5 hours it shows 12.54 volts. So if ever necessary when should I do a BMS reset, as soon as I stop or wait 1 to !.5 hours.

The vehicle smart charging system will only ever charge your battery to 80% of capacity even if you drive to the Moon and back !!

It is totally normal that after first stopping the engine and switching off that the battery terminal voltage will be lower than its true value since all of the vehicles modules are still fully active and are drawing a considerable load from the battery. Over a period of up to 30 minutes after locking the car the modules will all eventually enter a 'sleep' mode and the load on the battery becomes less than 200mA and therefore the battery terminal voltage will return to it's true State Of Charge. All of this is monitored by the BMS and so resetting it will only serve to wipe out useful stored data.

Your off load voltage after settling time is very good at 12.54V and well above the expected normal value, so no need to be concerned.

4 hours ago, unofix said:

The vehicle smart charging system will only ever charge your battery to 80% of capacity even if you drive to the Moon and back !!

It is totally normal that after first stopping the engine and switching off that the battery terminal voltage will be lower than its true value since all of the vehicles modules are still fully active and are drawing a considerable load from the battery. Over a period of up to 30 minutes after locking the car the modules will all eventually enter a 'sleep' mode and the load on the battery becomes less than 200mA and therefore the battery terminal voltage will return to it's true State Of Charge. All of this is monitored by the BMS and so resetting it will only serve to wipe out useful stored data.

Your off load voltage after settling time is very good at 12.54V and well above the expected normal value, so no need to be concerned.

 

Thanks for that all my questions answered and that chart is very useful and I shall keep a copy of that for future reference. Thanks again