Nice guide with constructive comments. Thanks.
Both my strips broke at about 5-10 cm of pulling. Heart sank. I repeated the following: heat from hair dyer for about 1 min until the case was hot to touch, IKEA card edge to pry the battery along its length, reheating when the case cooled. Moved onto a stiffer/ thicker credit card type item once I could get it under the battery. Took me about 20-25 mins but with new confidence it could easily be done in 10 minute; I erred on caution since first time. I just used two 3 mm wide strip of double sided tape to secure the battery. Once i removed the film I heated up the case once again the soften the new adhesive before placing the battery. Working fine.