If you have a tech look at the system have him/her check the keyboard cable. It may be that the cable is not fully engaged and happened during the battery replacement.
Hello, my laptop skips keystrokes - once about every two phrases I'd say. This is incredibly annoyng since I write many emails per day, and I also code. It's taking a heavy toll on my produtivity, This has been happening ever since I had my battery changed about a month ago - I noticed it from the same day the change took place. I took it back to the technicians but they seem to have no clue about what to do - and deny the battery has anything to do with it.. (The battery is Dell original and the repair place is Dell certified) Have been researching the issue, with no luck, currently looking for other technicians for help - and so I figured I'd also post here, this issue is really stressing me. If anyone has some helpful info please share 
Dell XPS skipping keystrokes (after battery change)