Spare battery for Canon IXUS 70, what do you suggest?

Consider the "Impact" brand, as sold by B&H Photo. I got one as a spare from them, but I don't know about your suppliers in Europe.

It has 900 mAh capacity instead of the stock battery's 760 mAh. I can't say if it lasts longer or not. I can't keep track of how much I use or do not use the flash, so it would not be fair to compare. It ought to last longer under identical conditions, though. I do seem to get a few frames more warning that the battery is low before the camera goes dead on me. In other words, with the Canon battery, I can only shoot 5-6 more pictures once I notice the battery icon and with the Impacy battery, I can shoot maybe 15-20 more.

It doesn't hurt that it costs half as much as the Canon battery, either.

I bought my spare nb-4l from adorama.com
$19.95 - it works fine.

I would buy one like the one that came with your camera. Generic ones may work okay, but may not. I know someone who bought a generic one, and it overheated and didn't work any more.

there are generic ones that are cheaper