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Home Ni-Cd NiCAD (Nickel Cadmium) - has memory effect
NiMH (Nickel Metal Hydride) - higher capacity and are mostly memory free
Li-Ion (Lithium Ion) - highest capacity and the lightest weight, memory-free.
Li-Poly (Lithium Polymer). ultra-lightweight & does not explode. memory-free.
Sealed Lead Acid (SLA) - Heavy, Shorter life, must be kept at full
 charge during storage.
Alkalines - Disposable, inexpensive.
Nickel oxy-hydroxide similar to alkalines. Better performance in a digital camera,
worse in a CD player.
Both NiCd and SLA batteries can be severely damaged by being
deeply discharged to down below 75% of their rated voltage

• For gear with a high power drain (Video camera) or for devices you use often, rechargeable (NiMH) batteries are much more economical than disposables.
• NiMH cells discharge when they're not in use, so they're not the best choice for battery-powered devices that often sit idle.
• For a digital camera, buy disposable lithium. They retain most of their power for years when in storage.
• low- or medium-draw gear e.g. a CD player, buy a highly rated alkaline.

	NiCd	NiMH	Lead Acid	Li-ion	Li-ion polymer	Reusable Alkaline
Gravimetric Energy Density (Wh/kg)	45-80	60-120	30-50	110-160	100-130	80 (initial)
Internal Resistance (includes peripheral circuits) in mW	100 to 2001 6V pack	200 to 3001 6V pack	<1001 12V pack	150 to 2501 7.2V pack	200 to 3001 7.2V pack	200 to 20001 6V pack
Cycle Life (to 80% of initial capacity)	15002	300 to 5002,3	200 to 3002	500 to 10003	300 to 500	503 (to 50%)
Fast Charge Time	1h typical	2-4h	8-16h	2-4h	2-4h	2-3h
Overcharge Tolerance	moderate	low	high	very low	low	moderate
Self-discharge / Month (room temperature)	20%4	30%4	5%	10%5	~10%5	0.3%
Cell Voltage (nominal)	1.25V6	1.25V6	2V	3.6V	3.6V	1.5V
Load Current -    peak -    best result	20C 1C	5C 0.5C or lower	5C7 0.2C	>2C 1C or lower	>2C 1C or lower	0.5C 0.2C or lower
Operating Temperature (discharge only)	-40 to 60*C	-20 to 60*C	-20 to 60*C	-20 to 60*C	0 to 60*C	0 to 65*C
Maintenance Requirement	30 to 60 days	60 to 90 days	3 to 6 months9	not req.	not req.	not req.
Typical Battery Cost (US$, reference only)	$50 (7.2V)	$60 (7.2V)	$25 (6V)	$100 (7.2V)	$100 (7.2V)	$5 (9V)
Cost per Cycle (US$)11	$0.04	$0.12	$0.10	$0.14	$0.29	$0.10-0.50
Commercial use since	1950	1990	1970	1991	1999	1992

Source: What is the perfect battery? by Isidor Buchmann, President Cadex Electronics

1. Internal resistance of a battery pack varies with cell rating, type of protection circuit and number of cells. Protection circuit of Liion and Li-polymer adds about 100mW.
2. Cycle life is based on battery receiving regular maintenance. Failing to apply periodic full discharge cycles may reduce the cycle life by a factor of three.
3. Cycle life is based on the depth of discharge. Shallow discharges provide more cycles than deep discharges.
4. The discharge is highest immediately after charge, then tapers off. The NiCd capacity decreases 10% in the first 24h, then declines to about 10% every 30 days thereafter. Self-discharge increases with higher temperature.
5. Internal protection circuits typically consume 3% of the stored energy per month.
6. 1.25V is the open cell voltage. 1.2V is the commonly used value. There is no difference between the cells; it is simply a method of rating.
7. Capable of high current pulses.
8. Applies to discharge only; charge temperature range is more confined.
9. Maintenance may be in the form of 'equalizing' or 'topping' charge.
10. Cost of battery for commercially available portable devices.
11. Derived from the battery price divided by cycle life. Does not include the cost of electricity and chargers.

Lead-Acid

There are specalized types of Lead Acid batteries for these purposes. See the Battery page in the Auto section for more information on Lead-Acid batteries for cars and trucks.

Types:

• Flooded/wet cell Lead Acid - Typical car battery with 6 2V cells and caps on top for adding water. Called flooded because the lead plates are flooded with liquid Sulfuric acid (H₂SO₄).
• Sealed Lead acid (SLA) or Gas-recombinant VRLA (Valve Regulated Lead-Acid) batteries here are "sort of" sealed. They still should be kept top side up. There is still a vent for Hydrogen gas to escape, but a twisted vent that usually stops any acid leaks.
  Their greatest disadvantage is the high initial cost (two to three times over wet low maintenance) but arguably can have an overall lower total cost of ownership due to a longer lifetime and no "watering" labor costs.
  • AGM: Absorbed Glass Mat batteries.
    AGM batteries are also sometimes called "starved electrolyte" or "dry", because the fiberglass mat is only 95% saturated with Sulfuric acid and there is no excess liquid.
    The plates in an AGM battery may be flat like wetcell lead-acid battery, or they may be wound in a tight spiral.
    They are being used in race cars and motorcycles because of vibraation resistance and educed likelihood of acid-spilling during accidents.
  • A gel-cell is a type of lead acid battery in a sealed case with a gelled electrolyte. They are "valve regulated", which means that a tiny valve keeps a slight positive pressure. Gel cells are more suitable in applications where the battery may be in different positions (as they can't spill electrolyte) and where they are not regularly inspected for leaks and electrolyte levels.
  • Carbon Foam Lead Acid batteries:
    A new taechnology which replaces the heavy lead grids with a graphite foam. Reticulated vitreous carbon ("RVC") plates are created and a lead tin alloy is deposited on the RVC plate by electroplating. Battery paste is applied onto the individual RVC plates, and they are cured.
    See FireFlyEnergy.com

Most smaller deep cycle batteries (including AGM) use Lead-Calcium plates for increased life, while most industrial and forklift batteries use Lead-Antimony for greater plate strength.

Gel Cells - 3-225Ah - $2 - $7.50/Ah
Jump Start batteries (Gel cells with jumper cables, lights, - 15-17Ah
Deep Cycle wet cells - 50 - 225 Ah - $1 - $2.50 / Ah
Deep Cycle Industrial wet cells 300-1800 Ah - $2 - 3.30 / Ah
Lead-acid battery prices have been fluctuating frequently due to the changing cost of lead.

Charactistics

• Lead Acid:
  Typical 12-volt lead-acid batteries have a voltage of about 14 volts when fully charged and 11 volts fully discharged.

  A name brand car/marine battery and charger which will turn off automatically ($60 + $50) will work much better than cheap battery and charger ($35 + $20).

  Buy a "deep discharge" or "deep cycle" if you buy lead acid. These are used on sail boats, on lakes for fishing, etc.
  Engine starting batteries perform poorly for communications because they are designed for short periods of high load. Deep cycle batteries are better for communications because they withstand long periods of slow discharge.

  Deep cycle or Deep discharge batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. This gives less surface area, thus less "instant" power like starting batteries need.

  Amp-hour ratings of deep cycle batteries are based upon a discharge rate at 1/20 capacity, expressed as C over 20". A marine battery rated 200ah at C20, when discharged continuously at 10 amps, at 80¡ F., sustains the load for 20 hrs.
  Most smaller deep cycle batteries (including AGM) use Lead-Calcium plates for increased life.

  Deep cycle batteries can't accept very high charging rates. If you charge from a car with a really hot alternator that can flow a lot of amps, you need to make sure your deep cycle battery can accept the charge rate.
  See Deep Cycle in Products
  

  Total charge time and current should not exceed 140% of battery capacity.

  A simple test load for small gel cells up to 20ah is a 50w, 12V marine/RV bulb or automotive drop light, which draws about 3.8A, equal to a mobile radio on low power a 5w transmit or a portable 2-meter hand held, plus a laptop computer. Two bulbs on a Y adapter simulate a mobile radio at 25w RF output and are a good test load for batteries to 30amp-hours. In a good battery voltage drop stabilizes quickly, does not fall below 11.5V under load and recovers quickly when the test load is removed.

• Gel Cell:
  Batteries using "recombination technology" (used in gel-cells) suffer from multiple failure modes, ie. premature dryout, thermal runaway, sensitivity to AC ripple to name a few. Their life is shorter than a flooded lead-acid battery.

  Gel cell longevity has a lot to do with the charging rate. One must charge these batteries very slowly with a 500mA trickle charger.
  Gel cells should never be charged at over 14V.

Links: (Lead Acid)
Car Batteries in Auto
Terms/Glossary in Auto.
Deep Cycle in Products
Charging in Tech
Gel-cell VS Sealed Lead Acid Battery for Astronomy at sci.astro.amateur group
Battery Guide at DiffLock 4x4
Camping Power Management Tips by George Schreyer;
Deep Cycle Battery FAQ, an extraordinarily useful, informative, and comprehensive webpage, by Northern Arizona Wind & Sun, Inc., with a list of helpful links at the end;
CAR AND DEEP CYCLE BATTERY FAQ, compiled by Bill Darden: a plethora of links to informative articles;
Deep Cycle Battery FAQ at N. Arizona Wind&Sun Vector Jumpstart & Power Supply 17 AH

Car Batteries in Auto
Links (Other):
Terms in the auto battery page
Battery sources at products
New Technology Batteries Guide: Fundamentals of Battery Technology
What is the perfect battery? by Isidor Buchmann, President Cadex Electronics
Computer Battery Help at ComputerHope.com
Battery Related Questions at AtBatt.com
How Batteries Work at HowStuffWorks.com
Charging in Technology here
Best Batteries and Match the batteries to your gear at ConsumerReports.org
Battery Power Basics at The Connection fron North American Emergency Communications (NAEM)