Difference between revisions of "Rechargeable"

This is a new (2009) battery chemistry. It requires a special charger due to the higher nominal voltage of NiZn cells. They are 1.6V nominal, but are charged to 1.8V to 1.9V and are recharged at 1.5V. PowerGenix makes the batteries and chargers, claiming 2500 mWh of capacity (see [[battery capacity]]). Quantaray is another company that makes NiZn AA cells. The higher voltage may make some flashlights brighter than on NiMH or Alkaline cells, but could also damage devices, especially if they use a number of AA cells in series. NiZn cells are advertised as capable of 200 full charging cycles, which is less than LSD NiMH cells.

Lithium polymer batteries are typical in mobile phones, where they offer higher density of charge storage. In other words, more amp hours can be stored in less size and weight. They can also be referred to by the chemistry of the anode (positive) which is lithium cobalt oxide (LiCoO₂). They do not suffer from the "memory effect." However, they cost more, and are not as long established as the older AA, C, D, types typical in torches.

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.

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 milliam 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. In the past, 10440 cells did not come with protection circuits because they were too small. However, some have recently (late 2009) come on the market (they may be too long to use in most AAA lights).

Li-ion cells are available from DealExtreme or KaiDomain under suspiciously similar brandnames like Ultrafire, Trustfire, etc., but most CPF members recommend AW cells (available through some online dealers and directly from AW via [http://www.cpfmarketplace.com/mp/forumdisplay.php?f=13 CPF Marketplace/Dealers] under the latest AW's LiIon Batteries Sales Thread) which are of consistently higher quality and have better protection than the cheaper cells. 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.

Li-ion cells have fairly low self-discharge, but in order to prolong the life of the battery, should be stored partially discharged.

Offers about a 20% increase in charge density over Li-ion, but again, offset by cost. These batteries are usually rectangular in shape and are used more often in MP3 players and cell phones than flashlights. They can be made in almost any shape if required, instead of a metal can typical of lithium ion cells, they are a bunch of chemicals in a plastic bag usually with a rigid case around them. Several laptop batteries (notably, Apple's ones) are now made of LiPo cells rather than the 18650 cells typical of older laptop battery packs. This is unfortunate for the consumer as it makes it almost impossible to replace the cells in a battery pack as it will probably be impossible to source the same LiPo cells that the original manufacturer used.

===Lithium Iron Phosphate (LiFePO4) - 3.3V/cell===

New LiFePO4 batteries have about 20% lower energy density than Li-ion, but they become even after about a year of use. LiFePO4 also have much longer life (typically about 10 years, as opposed to 2-3 years for Li-ion) and can endure almost double charge/discharge cycles than Li-ion. They also have lower self-discharge rate, and 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).