Tescos do a great little gadget for testing batteries ( Draper brand )
I got one before christmas for only 99cent it tests batteries all different sizes and you can also use it to check light bulbs and fuses.
They might still have them.
Regards,
Fries.
*Edit* I found this link, when I got it it was reduced to 99c.
http://direct.tesco.com/q/R.100-1575.aspx