Patek Philippe Calatrava

Hello and help with my watch ?'s.
I inherited this watch and no nothing about it except it's not running. It's style is "Invicta Professional Elite Swiss Chronograph and is probably 10yrs+ old. It's stainless steel and is all black finish and water resist to 20atm. As I stated-it's not running-I would guess it needs a battery replacement! I'm not rich-and sending it to Invicta repair service for probably $50 or more just to repalce the battery is steep for me. I think I could remove the case to replace the battery myself-but,if just removing the case cause any damage such as it loosing it's water resistency,etc.? Any help would be appreciated. Thanks

OM Question
does anyone know how big of a wrist the bracelet on an Orange or Black Monster will fit?My step son is a pretty big kid and I'm wanting to get him either an Orange or Black monster for his B-day.I guess I should have gotten his wrist size before asking this so I could have just asked, Does anyone know if an OM will fit a X size wrist? .

Looking ar getting a used roo panda what are papers what am i looking for?
Can someone post a pic of all papers that i need? When people refer to papers what are we talking about here exactly? Sales invoce, certificate of authenticity?Please post a picture of examples what these papers have to look like Thank you

Some AP15400 questions
Don't mind my asking, but I will like to ask existing owners of 15300 and 15400 Royal Oak owners some questions. 1) How's your 15300 / 15400 holding up? Any accuracy or reliability issues so far?2) Does the polishing fade over time or stays brand new? 3) Do you use it as a daily wearer? Is it tough enough for daily wear? While it is undeniably beautiful to me, it also looks kind of delicate. 4) Is it true that the Blue Dial version is more prestigious because it is more rare?5) With the polished surface reflecting light, do you find it too blinky to wear on occasions that a blinky watch might not be suitable, such as formal business meeting, visiting clients etc?6) What will be expected service cost I will be expected to pay be like once it is due for full service? And how's AP's after sales service?7) Does AP warrant availability of parts further down the road like 20 years, 30 years etc?8) If given the chance to repeat the purchase again, will you do it? Or you will choose another br

korean patek pricing?
know they tend to run a fair bit higher in korea but was wondering if could get some help as far as pricing in nautilus and aquanaut models.