Yes, they all must have battery-back up to ensure they continue to function if they lose mains power. Horizontal fire curtains, due to the direction of closure, require a secondary power source to ensure deployment. This secondary power source is a rechargeable, 30-minute, battery backup, so you have peace of mind that no matter what the situation, your space will be protected. This curtain cannot utilise a gravitational fail-safe due to the direction of closure. Vertical and concertina fire curtains also have a battery back-up which means they will stay in their ‘open’ position for 30 minutes after  loss of mains power e.g. in a fire situation. This is to allow safe evacuation prior to the fire alarm signalling them to close (deploy). They also have gravitational fail-safe to ensure deployment after the 30-minute battery back-up is depleted.