If you are using alkaline batteries, remove them from the flashlight if it will not be used for a long time, otherwise they will leak and cause problems. Keep them close to your flashlight so you can easily find them. Try sticking batteries to the body of the flashlight.
Professional advice: The most efficient flashlights are built specifically to use lithium-ion batteries or have non-removable rechargeable batteries that won’t do you any good if the power is out for a long time. Rechargeable AA nickel-metal hydride (NiMH) batteries retain their performance better over the life of the battery, while alkaline batteries degrade more as they are discharged, so buy multiple batteries. Panasonic Eneloops for $41. They’re better for the environment, but if they run out of battery, you can still use regular alkaline AAs.
You may prefer to keep a headlamp handy. Petzl Actik for $40. – my favorite model that has never let me down, from snowy mountains to dusty deserts. It runs on three easily accessible AAA batteries and has three brightness levels, the brightest of which is more than enough for home emergencies.
Coleman discontinued our previous favorite Divide+ Push Lantern, so $19 Coleman 4D Camping LED Light is the next best choice for a small amount of coins. Flashlights don’t do a good job when you need to light up an entire room or if you need your hands free for a task. This base flashlight offers a single 54 lumen setting with a runtime of 175 hours on four D-cell batteries. It sounds like a lot, but compared to other full size battery powered flashlights like the Coleman Twin LED flashlight which uses eight D-elements, it is economical. 54 lumens isn’t what I’d call bright, but it’s good enough for most tasks, even reading, while maintaining battery life.
If you’re looking to conserve batteries, or just prefer to spend your time with the soft flicker of a candle, keep a spare emergency candle or two. $10 Coghlan 36 Hour Survival Candle has three wicks, the service life of each of which is 12 hours. Keep a lighter or a few matches nearby.
In most cases, the water supply will work even during a power outage. But major natural disasters can disable or damage it, and you could end up with dirty water. $81 Grayl Ultralight Compact Cleaner is a durable and fast single person filter that lasts for 300 uses – 40 gallons in total – before you need to change the filter. This is what I trust when I travel to countries where there is no guarantee of water sanitation.