I'd like to keep a flashlight by my bed for home safety. I intend to only use it in emergencies. Since it's for a home safety emergency, I want to keep the battery stored in the flashlight so it's immediately usable. The flashlight I have is designed to take a 18650 battery or three AAA cells. To avoid battery corrosion and keep my flashlight functional in an emergency at least for a short time, what is the best type of battery to use in this situation? Lithium-ion? Non-rechargeable lithium? Alkaline? Nickel metal hydride? For how long is it safe to store that kind of battery in the flashlight?

  • \$\begingroup\$ I Google: "Longest lasting battery" and immediately a suggestion is made. Did you try that? \$\endgroup\$ – Bimpelrekkie Nov 9 '20 at 15:50
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    \$\begingroup\$ All batteries will eventually fail. Have you considered a battery-less flashlight? Such as those that can be shaken or wound to recharge. \$\endgroup\$ – rdtsc Nov 9 '20 at 16:01
  • \$\begingroup\$ @Bimpelrekkie, yes, I looked for answers, but I'm not asking about which battery generally has the longest shelf life or which has the highest capacity. I'm asking about a more specific situation. If you know of a Google result that answers my question, please let me know. \$\endgroup\$ – aswine Nov 9 '20 at 16:03
  • \$\begingroup\$ @rdtsc, That's a good suggestion. I'll look into it. I'm wondering if it would take too long in an emergency to charge? \$\endgroup\$ – aswine Nov 9 '20 at 16:09
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    \$\begingroup\$ The suggestion you would get from Google are to use Lithium based AA (they also exist in AAA form factor) which have a 20 year shelf life. Explain how your situation is any different as I do not see the difference. You're essentially storing the batteries inside a flashlight so shelf life is what matters. \$\endgroup\$ – Bimpelrekkie Nov 9 '20 at 16:28

Don't use any sort of rechargeable cells. They will be flat through self-discharge by the time you use them.

Non-rechargeable lithium cells aren't common in the size you want, but if you can source some, then they will last many years.

Otherwise, get brand new alkaline cells from a reputable manufacturer. Check the "install by" date on the betteries or the packaging, to make sure they have several years left on them. Even after their "install by" date, they will still work for a few more years, but will no longer last as long when you do use them.

  • \$\begingroup\$ Can you verify that rechargeable lithium batteries are safe to be stored in a flashlight? My flashlight's user manual specifically says that rechargeable lithium-ion batteries should be removed when the light's not in use. Also, as I mentioned in an above comment, I've had trouble with alkalines corroding in flashlights. \$\endgroup\$ – aswine Nov 11 '20 at 13:58
  • \$\begingroup\$ @aswine they always say that. It ensures that if the battery does leak and damage the flashlight, they can say it's your fault. The battery is no more likely to leak inside the flashlight than outside it. \$\endgroup\$ – Simon B Nov 11 '20 at 14:56

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