If you check on Amazon you will see that there are batteries available for £49.99 that have 5 star reviews.
toolsdown Replica Makita 18v 3.0Ah LI-ION battery BL1830: Amazon.co.uk: DIY & Tools
They are not FAKE, as they are not marketed as original Makita batteries, but as compatibles. I myself have 2 and they are excellent, indistinguishable in use from the couple of genuine Makita ones that I own.
I'm not suggesting that there aren't some dodgy ones out there, probably on FleaBay, but at least on Amazon you can see some reviews of what others think of them. You are also pretty much guaranteed to be able to get a refund if you want, as Amazon bend over backward to keep people happy. Well, that has been my experience anyway ;-)
Cheers
I don't know anybody who has had a problem with a makita battery, and i don't know anybody who has had a good "non makita" battery. it wouldn't be hard for someone (the company selling the batteries to fabricate those 7 reviews on amazon, it seems a bit suspect that they are all slating makita batteries, but i've never heard of a problem.