Question 1

how long is the strap?

Accepted Answer

The strap will be 7 - 7 1/2 inches long.

Question 2

Where to buy battery

Accepted Answer

Any place they sell watches.   I'm not sure where you live but there are watch shops here.  People also buy watch batteries at Wal-Mart, Fred Meyer and an actually battery store here in town

Question 3

Doesn't come with battery . If so, why the watch doesn’t work?!

Accepted Answer

Not sure why the one you are looking at doesnt work?  The one I purchased was a gift and she loved it!!   I copied the description and pasted below  it comes with a battery and a display case .. 
Product Description
Watch Sizing Guide Find a confident ensemble with the addition of this sleek Michael Kors® Pyper watch. Stainless steel case. Leather strap with adjustable buckle closure. Round face. Three-hand analog display with quartz movement. Dial features gold-tone hands and hour markers, minute track, and Michael Kors detailing. Water resistant 165 feet. Display case included. Imported. Measurements: Case Height: 38 mm Case Width: 38 mm Case Depth: 7 3⁄10 mm Band Width: 17 mm Band Circumference/Length: 8 3⁄4 in Weight: 1.2 oz

Product details
Is Discontinued By Manufacturer ‏ : ‎ No
Product Dimensions ‏ : ‎ 3.54 x 3.54 x 3.54 inches; 3.53 Ounces
Item model number ‏ : ‎ MK2797
Department ‏ : ‎ womens
Batteries ‏ : ‎ 1 Lithium Metal batteries required. (included)
Date First Available ‏ : ‎ February 1, 2019
Manufacturer ‏ : ‎ Michael Kors Watches
ASIN ‏ : ‎ B07MBGTZ5Y
Country of Origin ‏ : ‎ China
Best Sellers Rank: #23,275 in Clothing, Shoes & Jewelry (See Top 100 in Clothing, Shoes & Jewelry)
#29 in Women's Wrist Watches
Customer Reviews: 4.7 4.7 out of 5 stars    8,588 ratings
Product guides and documents
User Guide (PDF)

Question 4

I received the mesh rose gold 38mm watch for christmas, but my wrist is very small. is there any way to adjust the band for the mesh watches?

Accepted Answer

Check out the link below to find out how to adjust the mesh strap on your watch!

https://www.youtube.com/watch?v=bkxYvMAgUtE

MK2797 Women's Analogue Quartz Watch with Leather Strap

Description

Specifications

Reviews

Common Questions

ASIN	B07CJDP3LP
Batteries	1 Lithium Metal batteries required. (included)
Best Sellers Rank	#234,451 in Fashion ( See Top 100 in Fashion ) #3,090 in Women's Wrist Watches
Country of origin	China
Customer reviews	4.6 4.6 out of 5 stars (1,844)
Date First Available	14 August 2018
Department	Womens
Is Discontinued By Manufacturer	No
Item model number	MK2747
Manufacturer	Michael Kors
Product Dimensions	3.6 x 4.1 x 3.7 cm; 100 g