Hi @sammiie43,
Thanks for getting back to me.
The transformer will get warm when running the computer and the battery is being changed at the same time.
If you fell it is getting too hot, please use the following http://www.hp.com/contacthp and create a case for your issue and contact HP. If you live outside the US/Canada, please click the link below to get the contact information for your region.
http://www8.hp.com/us/en/contact-hp/ww-phone-assist.html
Please keep me informed of how things went.
If you require further assistance, let me know and I will gladly do all I can to help you.
Please let me know if this resolves the issue by marking this post as "Accept as Solution".
To simply say thanks, click the Thumbs up below! 
Thanks.