Heads up on laptop batteries and voltages (particularly HP550's)
It's a long story so I'll try shorten it. We needed replacement batteries for our HP550 model laptops. I go to a site that lists 3 different batteries when navigating to them via our model name, 2 have the 10.8 voltage, 1 has the 14.4 voltage, I go for the 14.4 voltage ones. I assumed they would work with our model, read all the on-screen details, nothing to suggest they wouldn't work. A few months down the line these batteries are coming back to us as dead???. Spoke to the supplier and discover there are two different types of HP550 around, one that comes with a 14.4v battery and one that comes with a 10.8v battery. There is no known way just from looking at the laptop that you can tell these apart. Our model of HP550 comes with an 10.8v battery and the 14.4v battery is incompatible with it. So I argue with the supplier and say there was no warning on their site about this (taking screen shots beforehand of their site), but yes there was, after coming back from holiday to resume the dispute I'm advised there is a live link next to the word "voltage". True enough, didn't notice this before, but if I click on it, it explains I need to check the voltage is compatible.
So the long and short of it is: when ordering replacement batteries for laptops, go for the same voltage batteries as the originals that were supplied in the laptop to ensure compatbility and don't make the mistake I made. Unfortunately we ordered 21 of these 14.4v batteries and it looks like they're all knackered.