Exclamation [Q] Help:Battery Drop after updated to .402?

So last night i plugged in my z2 to my laptop and download the update 402 via sony pc companion. I left it overnight and this morning when it finished updated, i switched on the phone it was at 99%.

After a few mins i look back, it dropped to 74%!
Has anyone experiencing the same issue? is this normal? is this update bad for the battery?

anyway i did a factory reset, it was still new anyway so not much things on it yet.
ps, i did not lose my X-reality.Its still there