MacBook Pro A1229 shuts down suddenly at 50% Battery capacity left

Hi,

I bought a new battery for my 17¨ MacBook Pro A1229 (Bought Dec. 2007). I followed instructions that came with the battery:

First time use: Let the battery run down to 2% before charging and then charged the battery fully to 100%.

I then proceeded to use my MacBook. At 50% battery charge left, it suddenly shut down completely. I then tried to reload the battery fully to 100% once more, then left the MacBook with it's charger plugged in for 2 hours. When I then used the MacBook, the same happened again; at 50% battery charge left, it shut down.

I the proceeded to reset the SMC and PRAM. This did not fix the problem.

I then proceeded to return the battery to the supplier and received a new identical battery. Followed instructions as listed above; the problem persists - The MacBook Pro shuts down when running on battery at 50%