Imo, the choice of battery depends on how long you want to be able to wait before replacing or recharging
bottom line, if you don’t want to think about it for years, use Ultimate Lithium
LiIon, if replaced every month, can work
NiMh, replaced every 6 months, can work
LiIon, does not need to be replaced for 15 years
storage at 140F
Primary Lithium retains more than 90% capacity after 15 years
Secondary Lithium drops to 60% capacity in 3 months
NiMh drops to 70% after 1 year
how hot does it get in a car, rule of thumb, 50 degrees F higher than outside… so a car will get to 140F if it gets to 90F outside.
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derived from these links:
“_LiIon, 60% after 3 months
NiMh, 70% after 1 year_”
http://www.led-resource.com/2011/10/introducing-energizer-ultimate-lithium-runtime-tests/
Ultimate Lithium “Retains 90% capacity after 15 years.”
risks of over discharge of LiIon, potentially explosive failure of LiIon,
“Li-ion cannot dip below 2V/cell for any length of time. Copper shunts form inside the cells that can lead to elevated self-discharge or a partial electrical short. (See BU-802b: Elevated Self-discharge.) If recharged, the cells might become unstable, causing excessive heat”
how hot does it get in a car?
http://acprocold.com/blog/hot-car-get/
“After 90 minutes, the average temperature difference is 48 degrees. On a 90-degree day, that equates to 138 degrees
…
Interestingly, these temperature increases are roughly the same no matter what the outdoor temperature is. Even on a beautiful 75-degree day, the temperature after 90 minutes will be over 120 degrees. If you’re in a desert heat wave and the outside temperature is 110, expect a car interior around 160 degrees.”