V15, new head, battery life halved

Hi, I bought a V15 a couple of years ago. Within a few months of purchasing I did have to take it to be repaired, and they replaced the motor and dust chamber component, funnily enough the one I bought was a purple colour, and the one I had returned is an aqua and gold colour. So I’m actually not sure if I got back an earlier model than the one that I had purchased… Anyway fast forward, the red clip on the motor head broke and Dyson very kindly sent me a new motor head for the vacuum (I have a daughter with severe dustmite allergies THANK YOU!!) so it’s really important that I do vacuum daily. However I noticed when I use it now it makes a different noise (higher pitched) and my battery life has dropped down on the normal mode from around 35 minutes to 15 minutes which is what I used to get when it was on full power - I struggle to vacuum my entire house in this time frame. Has anyone else come across this? Thanks for reading and hopefully answering !