Davo, You only need a guaranteed power supply, it does not prescribe a battery. A battery may well be a very good provision but as far as the legislation is concerned you need neither if your risk assessment does not require you to have an alarm and the responsible person can satisfactorily raise the alarm another way. I am sure like me you would say this is not an option but the legislation gives the responsible person exactly that option.
Which is my point..the provision of any system is risk appropriate and it is for the competent person to provide suitable and sufficient arrangements to meet the objectives of the fire safety strategy. If the competent person provide fire safety signs that are not understood, have no provenance and can be misleading it has to be a matter of professional liability. The annex illustrations in an EC Directive, like the guaranteed power supply are to be interpreted by a competent person into satisfactory robust provision. This is where code and standards sit and should stand professional scritiny and test.