First of all thanks for all the help this forum has supplied over my 6 months gs450h ownership.

The message CHECK HYBRID SYSTEM was displayed, after replacing the normal 12v battery. After going online I found someone in Northhampton Hybrid Battery Solutions, Richard Farewell, that would check the battery condition and replace the duff cells. As the car was drive able he tested the cells at his workshop, to find basically all was ok. But a fault code indicating faulty heat sensor was shown.

After a brief discssion I told him that I had not reconnected the Heat sensor embedded in the original panasonic battery. He said this was the problem and gave instructions to reset the fault code. On my return I reconnected the sensor. Disconnected the negative terminal for 2 minutes reconnected and all was ok.

Hope this helps someone, and if you do have issues with the hybrid battery you will consider Richard his email is enquiries@hybridbatterysolutions.co.uk
I hope giving this is acceptable.