replacing Li-Ion batteries

[Un4tural]

so i got my nook hd+ (the 9" full HD screen one) for a while now but the battery is kicking the bucket (charge it fully after few minutes of use just shows 1% until it decides to turn off entirely...) and replacement battery costs 13£, now I'm not very good at magical pixie compatibility, but i thought, if the battery is same voltage rating, it should work if i replace with one from a different device? as far as i can tell it would report wrong battery capacity cause probably it uses some different protocol to report battery/voltage remaining? 

 

was thinking of grabbing a battery from a different device, maybe a higher capacity one and mcguiver'in it in there, would probably be cheaper and last longer, as only ones on ebay are used ones, which means they'll fail really really soon either way, due to the nature my battery seemed to fail (sudden and conclusive) versus the more gradual decrease in capacity...

 

so i'd like to check with people who posses more knowledge in the art of pixie taming if i need to purchase exact one made for the tablet, or would any work with similar battery charging or lack of circuitry? replacing the whole tablet seems like an awful shame as the screen is really good and albeit slow it can display full HD movies no problem, satisfying my tablet needs....