Macbook Pro battery powers down at random

I recently bought a new battery for my 2.16Ghz 15" Macbook Pro from ebay. I was replacing the original battery that was about 4 years old and couldn't hold its charge for more than 40 mins.

The new battery works fine off the AC power but cuts out at random and without warning when running off its own power supply. It is not a case of the battery simply running out as when I turn the machine back on I find the battery still has fairly high % of charge left (over 80% one time!).

I would try to calibrate the battery by running it down to 0%, letting it sleep and then recharging fully, but I don't really want to risk the inevitable 'power cuts' the battery would likely go through before getting to 0%.

These power outs cant be good for the machine.

Can anyone advise? And before you ask, yes, this is a legitimate battery (or at least it looks like one), with the correct model part for my Mac.

Would appreciate any help.
Many thanks.

Buying substitute batteries from eBay is risky at best. Many folks have found out that "exact" replacement batteries purchased off eBay are not what they claim to be. You save a few bucks but usually you wind up replacing the replacement. My advice is to return it if possible and get a refund.

Buy from here instead.

Regards.

My battery does the exact same thing as AJCardy's but it's a 3 year old battery on my MBP.
Just now purchased a new battery from OWC. Thanks for the link chscag! ;D