Battery icon with red slash???
 

I received a CS1 battery with my 8700 but had a CS2 from a previous model. I used the CS1 battery for 2 recharges but swapped to the CS2 as it seemed to hold more charge. Now when I insert the CS1 battery the device powers up with a dim screen showing a large battery icon in the centre with a red slash through it. Even if I charge the battery for hours it still doesn't disappear nor will the device power up. If I put the CS2 battery in, it powers up as normal.

Any ideas what this icon may represent?