I have to change the battery for my n800...
I found this on ebay http://cgi.ebay.co.uk/Q569-1500ma-Ba...hippingPayment

What do you think?Should I buy it or not?

I bought two batteries on Ebay from Hong Kong. From the picture you gave it looks identical to mine. One holds a charge for less than 1 hour. The second one works great! Both were just a few dollars (US). Even if I bought 5 batteries at a total cost of just $20, if only 1 works great, I am still ahead of the game.

Until of course it blows up in your IT...

Even batteries made for Nokia have had problems, life is a gamble.
http://www.wirelessgalaxy.com/researchcenter/46-million-nokia-cell-batteries-defective.asp

I bought a few identicale batteries also from ebay. I bought 3 for $5 each and with shipping it was only $20.

My OEM battery at full charge shows "when idle: 10 days, when in use: 7 hours"

cheap chinese knock off battery #1:
"when idle: 9 days, when in use: 5 hours"

cheap chinese knock off battery #2:
"when idle: 6 days, when in use: 2 hours"

cheap chinese knock off battery #3:
"when idle: 8 days, when in use: 4 hours"

OEM battery from my 770: "when idle: 10 days, when in use: 7 hours"

So yeh, with these fakes YMMV... greatly.

BTW, I bought a couple fakes for my nokia cell that looked real complete with hologram. If you look closely to the hologram sticker, it was a flower. The had taken cheap holos and die cut them.

I found that using the Tekkeon MP1800 externaly is the best option for me, I reduce how much I need to use the internal. But I have been looking for a better internal battery, not just a replacement but a HC battery that fits.

i bought one before couple days $10 shipped and it was suppose to be the orginal Nokia but used like New , but it is not Nokia its Chines . without any nokia logo .. so i dont have time to return it as i'm travling . but i might have to leave the seller neg feed back ..