OK I can see a few possibilities..
You might have replaced a bad battery with another bad battery (just because it's new don't assume it's any good)
you've replaced the battery with one of the incorrect type.
You have the time zone set incorrectly on your laptop and it's resetting the clock to the time it thinks it should be for the time zone it thinks its in.
Or, the on board clock has gone faulty, in which case, realistically, you'll just have to put up with it. though setting up internet time sync would alleviate the problem.