Change battery now check engine light is on?

This is not uncommon when there is a battery disconnect. So let's run through these couple of guides and see what comes back:

Let's start with checking for codes and see what is turning on the check engine light.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Next here is a guide that covers common things that go wrong after a battery disconnect:

https://www.2carpros.com/articles/everything-goes-dead-when-engine-is-cranked

This could be just some erroneous DTCs that get set when the battery is disconnected so what I would suggest is recording the codes and then clear them and see if any of them return.

If they return then we have an issue and can track them down. However if they don't then it was just due to the battery disconnect.

Let us know and we can go from there. Thanks