2 minutes ago, PetrolDave said:

Yes, it's the serial number that tells the BMS a new battery is fitted. If you don't change the serial number then the BMS will assume the old failing battery is fitted and is likely to start turning off systems to protect the old battery that's no longer fitted.

Gotcha. makes sense.

 

I've always wondered - If you trickle charge via a 12v accessory socket, does this bypass the batteries control unit? or does it know whats going on?

 

 

1 hour ago, Jono said:

does this bypass the batteries control unit? or does it know whats going on?

No and yes.