A head torch flashes briefly when you press the button at home. That proves it can light for a moment, not that it is ready for the walk. Test the controls and the batteries you will actually carry before the bag is packed.
Use the intended operating mode
Read the manufacturer’s instructions for battery type, charging, lockout and the meaning of any charge indicator. Confirm that you can select the ordinary walking mode without cycling through the controls in confusion. Do not shine a bright beam into another person’s eyes while testing.
Check the strap and housing for obvious damage, and inspect the battery compartment only as the instructions permit. Use compatible batteries or the specified rechargeable pack. A spare that does not fit the torch is dead weight rather than a backup.
Test the travel lock too
Some torches have a lockout function to reduce accidental activation in a bag. Practise enabling and disabling it before departure. A torch that seems broken at dusk may simply be locked, while one that switched on inside the pack may have used much of its charge.
Pack spare batteries securely so their terminals cannot contact loose metal, following the battery maker’s guidance. If the torch uses an integrated battery, plan an appropriate backup light or charging arrangement rather than assuming every power bank and cable will be suitable.
Check the manufacturer’s runtime information for the mode and conditions, but do not treat a headline maximum as a guarantee for your trip. Plan conservatively for delays and cooler conditions where relevant. A light does not make an unsuitable route or deteriorating weather safe.
Before leaving, have each person who may need a light operate their own equipment. Keep it accessible rather than buried beneath the contents of the pack. The best preparation is being able to find, unlock and use the light calmly before darkness makes those small tasks harder.