Rechargeable: Difference between revisions
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→Battery types: a little more info about li-ion and LiMn cells
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'''Important:''' ''***These are not the same as [[Primaries#Lithium|disposable lithium batteries]] sold by Energizer (Energizer e2 or Ultimate Lithium), Saft (who make it more confusing by selling 3.6V lithium cells that are not rechargeable), and other companies since those can not be recharged and will explode if you try it ([http://www.candlepowerforums.com/vb/showthread.php?t=250219 example]).***'' | '''Important:''' ''***These are not the same as [[Primaries#Lithium|disposable lithium batteries]] sold by Energizer (Energizer e2 or Ultimate Lithium), Saft (who make it more confusing by selling 3.6V lithium cells that are not rechargeable), and other companies since those can not be recharged and will explode if you try it ([http://www.candlepowerforums.com/vb/showthread.php?t=250219 example]).***'' | ||
Though there are other lithium ion chemistries (listed below), but usually when people talk about lithium ion batteries they are talking about lithium cobalt, LiCoO<sub>2</sub>, after the chemistry of the battery anode. They are available in a wide variety of sizes including CR123A, AA, and AAA. However, because of the higher voltage, Li-ion cells can only be swapped for NiMH or alkalines if the device manufacturer recommends it. Be careful! A fully charged li-ion battery has 3 times the voltage of a NiMH cell. Some flashlights that use two CR123A batteries can take a single 18650 battery (though this battery is wider than CR123A cells) which offers substantially more capacity than the two smaller cells together. | |||
Some brands of 10440, 14500, and 16340 cells are longer than their AAA, AA, and CR123 counterparts, so make sure you are getting cells that are not too long and that your light can deal with the size variance by reading the forums and reviews of the batteries. Just because a cell is sold as an 18650 does not mean it is exactly 65 mm long: some are 68 mm long. | Some brands of 10440, 14500, and 16340 cells are longer than their AAA, AA, and CR123 counterparts, so make sure you are getting cells that are not too long and that your light can deal with the size variance by reading the forums and reviews of the batteries and/or lights. Just because a cell is sold as an 18650 does not mean it is exactly 65 mm long: some are 68 mm long. | ||
Li-ion cells must be monitored more closely than other chemistries. If they are charged too high (above 4.2 volts) or discharged too low, they can overheat or cause a fire. Some good advice is that if you don't have a volt meter and aren't willing to monitor the cells during use and won't be able to watch the cells the entire time they are in a charger, then you shouldn't be using them. See [http://www.candlepowerforums.com/vb/showthread.php?t=235164 this thread] for safe use of li-ion batteries. Cells are categorized as being | Li-ion cells must be monitored more closely than other chemistries. If they are charged too high (above 4.2 volts) or discharged too low, they can overheat or cause a fire. Some good advice is that if you don't have a volt meter and aren't willing to monitor the cells during use and won't be able to watch the cells the entire time they are in a charger, then you shouldn't be using them. See [http://www.candlepowerforums.com/vb/showthread.php?t=235164 this thread] for safe use of li-ion batteries. | ||
Cells are categorized as being '''unprotected''' or '''protected'''. Protected cells include circuitry that will essentially turn the battery off if the voltage goes too high, too low, the drain is too high (the current drawn from a li-ion cell should not exceed twice the nominal milliamp-hour capacity in milliamps - so a 2000mAh cell should not be asked to produce more than 4000mA (4 amps)), or the polarity is reversed (not all protected cells protect for every one of those cases, and the voltage cutoffs vary as well). For this reason many people recommend protected cells. However, the low-voltage protection often kicks in only when the battery voltage goes below 3 volts, but 3.6 volts seems to be the point where most people recommend recharging the battery. The protection is there to prevent a fire, not to tell you when your battery should be recharged. See [http://www.candlepowerforums.com/vb/showthread.php?t=106242 this CPF Thread] for info about protection circuits. | |||
Li-ion cells have fairly low self-discharge, but in order to prolong the life of the battery, should be stored partially discharged. | Li-ion cells have fairly low self-discharge, but in order to prolong the life of the battery, should be stored partially discharged. | ||
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New LiFePO<sub>4</sub> batteries have about 20% lower energy density than Li-ion, but also have much longer life (typically about 10 years, as opposed to 2-3 years for Li-ion) and can endure almost double the number of charge/discharge cycles of Li-ion. They also have lower self-discharge rate, are able to deliver higher current, and are more resistant to thermal runaway. However, as they are not as popular as Li-ion, they are still somewhat more expensive. Because they can not be charged to 4.2V, they require a special charger (or hobby charger that can be set to 3.6V max). Walmart sells 3.2V AA-sized LiFePO4 cells by Westinghouse for solar lighting (so no charger included). | New LiFePO<sub>4</sub> batteries have about 20% lower energy density than Li-ion, but also have much longer life (typically about 10 years, as opposed to 2-3 years for Li-ion) and can endure almost double the number of charge/discharge cycles of Li-ion. They also have lower self-discharge rate, are able to deliver higher current, and are more resistant to thermal runaway. However, as they are not as popular as Li-ion, they are still somewhat more expensive. Because they can not be charged to 4.2V, they require a special charger (or hobby charger that can be set to 3.6V max). Walmart sells 3.2V AA-sized LiFePO4 cells by Westinghouse for solar lighting (so no charger included). | ||
===Lithium Manganese (LiMn) 3.7V/cell=== | ===Lithium Manganese (LiMn<sub>2</sub>O<sub>4</sub>) 3.7V/cell=== | ||
These cells allow higher drain (5C) than li-ion cells without some of the dangers. AW sells these as IMR, and Sony as Konion. They can be charged in most li-ion chargers, but some li-ion chargers will overcharge LiMn cells. LiMn cells should be charged at 1C to 2C. Due to lower overall capacity, these batteries fill a niche with flashlights demanding very high current where runtime isn't that important. While they are safer than lithium-ion cells, they can still be made to explode if provoked sufficiently, unlike the LiFePO<sub>4</sub> cells which cannot. | These cells allow higher drain (5C) than li-ion cells without some of the dangers. AW sells these as IMR (supposedly based on "LMR" for lithium manganese rechargeable, but the lower case "L" was mistaken for an "I" and never corrected), and Sony as Konion. They can be charged in most li-ion chargers, but some li-ion chargers will overcharge LiMn cells. LiMn cells should be charged at 1C to 2C. Due to lower overall capacity, these batteries fill a niche with flashlights demanding very high current where runtime isn't that important. While they are safer than lithium-ion cells, they can still be made to explode if provoked sufficiently, unlike the LiFePO<sub>4</sub> cells which cannot. | ||
=== Sealed Lead-Acid (SLA) - 2.0V/cell=== | === Sealed Lead-Acid (SLA) - 2.0V/cell=== | ||
A classic rechargeable battery where cells are hooked up in series to generate higher voltages. A 6V battery would have 3 cells and a 12V would have 6. They are sometimes used in [[Terminology#HID|HID]] lights, but not for more portable lights due to poor size/weight characteristics. However, SLA batteries are very reliable if kept topped up, cheap, and as such, often still used in cars, if not torches. | A classic rechargeable battery where cells are hooked up in series to generate higher voltages. A 6V battery would have 3 cells and a 12V would have 6. They are sometimes used in [[Terminology#HID|HID]] lights, but not for more portable lights due to poor size/weight characteristics. However, SLA batteries are very reliable if kept topped up, cheap, and as such, often still used in cars, if not torches. | ||