Difference between revisions of "Rechargeable"

A lot of confusion exists about battery voltage. Ordinary alkalines are rated to 1.5v, but typically are down to 1.2v when 50% used, and rapidly fall thereafter. This is why devices using alkalines often become less responsive over time (or dimmer with flashlights). Rechargeable NiCad or NiMH batteries are rated to 1.2v (starting at 1.4v at first) but will hold 1.2v until right at the end. You tend therefore to get a more consistent performance from rechargeable batteries. '''This improved consistency of voltage, is a major reason to prefer rechargeables for torch applications'''.

Three cells seem to work better in many flashlights. This is because most LEDs are designed to operate in the 3-4v range. 3 cells * 1.2 = 3.6v. No conversion circuitry is therefore required in 3 cell torches or if there is a circuit, it will work more efficiently. The bulb can be powered directly off the battery cells.

A good charger will use an appropriate charging rate (15 minutes is not appropriate), charge each battery individually, and will cut off when the battery is full rather than just after some period of time. It is very hard to find such a charger in stores. See [[Chargers]] for more information.

A newer generation of NiMH cells, called Low Self-Discharge (LSD), are able to hold a charge for a much longer time, claiming 75% charge after a year, instead of 50% discharge after 6 months for standard NiMH cells. The trade-off is that LSD cells usually have lower capacity (75%) than some non-LSD NiMH cells. These batteries are marketed as 'Pre-Charged' because they still retain much of their factory charge after months or years on a store shelf. Among LSD brands, Sanyo's [[Eneloop]] batteries have the best reputation and performance (retaining 85% of their charge after a year). Other brands include Duracell Precharged, Uniross Hybrio, Rayovac Hybrid, Powerex Imedion, Sony Cycle Energy, GP Recyko, and others. Because LSD cells are NiMH batteries, they can still be charged in any NiMH battery charger.

Introduced in 2008, Nickel-Zinc cells have already disappeared from the market. They require 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 and Quantaray made the batteries and chargers, claiming 2500 mWh of capacity (see [[battery capacity]]). 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. Some people found the performance of the cells to be inconsistent, while others saw good performance. In February of 2011, Powergenix said they would no longer make AA batteries and chargers and instead focus on industrial uses of larger NiZn batteries.

Though there are other lithium ion chemistries (listed below), but usually when people talk about lithium ion batteries they are talking about lithium cobalt, '''LiCoO₂''', after the chemistry of the battery cathode (these batteries are also sometimes called LiCo, LCR, or ICR). 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 and 18650's will not fit in some [[SureFire]] and [[4Sevens|Quark]] lights) which offers substantially more capacity than the two smaller cells together.

'''Recommended batteries:''' Many CPF members recommend AW (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) or Redilast cells (also on CPF) which are of consistently higher quality and have better protection than cheaper cells, but are very expensive ($12 each and up). Both of those brands use Panasonic NCR18650A 3100mAh cells which can also be purchased from other providers (but are still expensive). These are the highest capacity cells available in this size. Trustfire has a line of li-ion batteries with flames on the label that are a decent budget alternative in nominal capacities of 2400 or 3000 mAh though actual capacity will be less (roughly 2100 and 2600 mAh), however it is hard to find genuine ones even at DealExtreme which has been a reliable source in the past. eBay is a notoriously bad place to buy lithium ion batteries, with fake brand name batteries and false claims regarding capacity and battery protection. XTAR (using 2600mAh Sanyo cells) and Hi Max (using 2600 mAh Samsung cells) brands are better than Trustfire, but cost a little more ($7 each for XTARs via this [http://budgetlightforum.com/node/2476 BLF thread]). Here is [http://www.candlepowerforums.com/vb/showthread.php?330236 good review] of a number of li-ion 18650 battery brands, mostly higher end, plus [http://lux.yi.org/batt/ this older comparison] of budget brands.

New LiFePO₄ 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).

These cells allow higher drain ([[Terminology#C|5C]], up to 8C) than LiCo 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 (therefore they do not come with protection circuits), they can still be made to explode if provoked sufficiently, unlike the LiFePO₄ cells which cannot. As a budget alternative to AW or Sony cells, [http://www.bestinone.net/index.php?route=product/search&keyword=imr&category_id=0 Best In One] has generic LiMn cells in a number of sizes. These cells are also sold in the US by Shaotech at [http://www.shaotech.com/ his store] and on CPF Marketplace.

Panasonic makes 2250mAh batteries that are often called IMR, but seem to be a variation of LiCo cell with similar properties to LiMn cells. These have the product number CGR18650CH and are available from [http://callieskustoms.com/CalliesKustoms-Batteries.html Callie's Kustoms] or [http://www.intl-outdoor.com/panasonic-cgr18650ch-2250mah-liion-battery-p-291.html International Outdoor]. They do not usually have protection circuits but are not subject to thermal runaway like normal LiCo cells, and are capable of discharge rates of up to 10 amps.