A cell is the basic device comprising two electrodes separated by an electrolyte. The name of the cell usually includes reference to the materials used in the construction and the voltage of each cell depends on the chemicals used, eg an Alkaline Manganese AA 1.5 V, or a Lead-acid cell of about 2 V.
A battery is a collection of cells eg the PP3 9V (6 cells in series) or the Lead-acid car battery (typically 12 V, also 6 cells). Although the voltages are quoted usually as if they were accurate, mostly they are not. Voltages vary according to many factors eg temperature and state of charge.
There are 2 fundamental types of cells, Primary and Secondary. Primary cells are meant to be used once only, through to the discharged state and Secondary cells are designed to be recharged over and over (typically several hundreds of times). Some chemistry is suitable for use either as primary or secondary.
The number of different battery types, properties and applications is enormous, quite apart from the fact that each type comes in a variety of sizes, usually dictated by voltage and capacity. Capacity is measured in ampere-hours (Ah) or thousandths of ampere hours (mAh).

The following comments give a resume of certain types, within the limits of our knowledge, which you may wish to check with a definitive source elsewhere.

Primary:
Zinc Carbon: nominal 1.5 V, an old type, cheap and voltage varies considerably during use.
Alkaline Manganese: nominal 1.5V, ubiquitous replacement for zinc-carbon, higher energy more expensive.
Mercury: phased out in many applications because mercury is very poisonous, was/is used in small applications eg cameras, hearing aids.
Lithium: a wide ranging family with voltages varying from 1.5 V to 3.6 V, high energy density, voltage almost constant and very long shelf life. Sounds magic and indeed they are special but the downside is that Lithium is a very reactive element which can lead to explosive consequences. Do not attempt to charge unless explicitly specified and avoid short circuits. They are also very expensive.
Zinc Air: nominal 1.4V, as its name suggests must be exposed to the air (a seal is usually removed when first used), high self-discharge rate.
Silver Oxide: nominal 1.55V. Often sold as button cells, for use in calculators, cameras, watches etc where its stable discharge characteristics are valuable.

Secondary:
Lead-acid: nominal 2 V per cell, as used in cars, well known to be rechargeable, large capacities but lead is very poisonous. Can be either wet or dry. Probably the easiest to recycle because the large amount of lead in each battery has a value in the scrap metal industry. Lead-acid and Sealed Lead-acid (SLA) are used where relatively large energy ratings are called for but weight is not a major problem.
Nickel-Cadmium (Ni-Cd): 1.2 V per cell. Used extensively in rechargeable situations and because it exhibits a memory effect is either continuously trickle-charged or recharged after complete discharge (ie not partially discharged and then charged). Ni-Cd can be recharged a large number of times (say, more than a thousand), which may be the reason, unfortunately, why they are so popular. Cadmium is very poisonous, it would seem a good idea to avoid Ni-Cd wherever possible but has established a track record and is quite common unfortunately.
Nickel Metal Hydride (NiMH): 1.2V per cell. They are a new generation which can replace Ni-Cd and have higher energy density and longer life cycle, and don't exhibit memory effect, are usually charged with constant-current source. They do not contain the the most dangerous heavy metals so are more environmentally friendly than Ni-Cd. We feel that NiMH batteries should be used wherever possible to replace Ni-Cd. The disadvantage is that they cannot be recharged so many times as Ni-Cd (maybe less than a thousand), but unless you take care with the charge and recharge discipline needed with Ni-Cd you may well finish up with a battery which doesn't realise its potential and turns out to be inferior to NiMH (we speak from experience).
Nickel-zinc: 7 cells for 12V, is claimed to provide the lowest impact to the environment of any standard rechargeable battery technology mainly because of the absence of contamination from the dangerous heavy metals. They have lower cost than NiMH, are lighter and better performers than lead acid, have a high capacity per cycle and high cycle life and they also have low maintenance requirement. Size may be less than Lead-acid and about the same as Ni-Cd. For a good reference see the Evercel link on our Hazardous Waste page.
Lithium Ion (Li-Ion): used, as well as NiMH, in special applications eg laptop computers, are expensive to produce and hence to buy. They have the advantage that they have about twice the energy density of Ni-Cd and around 50% more than NiMH hence can be much lighter and smaller for the same capacity. They can be recharged for up to 1000 times approximately.
Lithium Polymer (LI-Polymer): apparently could become the battery of the future. They are reputed to have similar characteristics to Li-Ion but should be much cheaper to produce.

General Comments:
This has been one of the most difficult items to research. There have been significant advances in battery technology over the past few years and it is evident that the consumer culture has led to an increased use. Undoubtedly batteries provide us with benefits and conveniences which are valuable.
The battery market is a lucrative one and you can see that by surfing the net, indeed the information provided seems to be very protective of the market, with little to say, in the UK, about safe disposal. That some batteries contain metals which are deadly dangerous to humans and animals is undeniable; such dangers become reality when the items are disposed of in standard waste rather than recycled in some way. All this is compounded by the plethora of battery types (nothing to do with sizes) so that it is difficult to identify the scale of the dangers.
Three heavy metals, present in batteries, namely lead, cadmium and mercury pose serious health hazards. The effects of these elements on animals (including humans) are terrible, leading to debilitating pain with fatal consequences [for more detail on the dangers see the WEEE synopsis in the Electrical/Electronic section]. Yet what do we do to prevent haphazard disposal of them? Sadly in the UK, virtually nothing. We had expected the British Battery Manufacturers Association (BBMA) to provide us with information that would allow easy recycling. They have been active in setting up REBAT which purports to be interested in recycling and sets targets but when we last looked they suggested "in the first instance seek guidance from either the distributor ..... or the battery manufacturer or the appliance manufacturer". Sure, we good folks out here will do that, or maybe not be bothered. There is a long list of battery recyclers but doubt if that will be any use to the individual consumer. We are not impressed but decide for yourself and pay a visit:
There are some minor recycling schemes, including experimental council schemes. According to Which? (Feb 2003) Lancashire CC offers a scheme and Bristol is trialling the first kerbside collection scheme. Since Europe may aim for a 75% collection target by 2004 the UK has a lot to do and hopefully many more councils will adopt the kerbside approach (Oh, if only!). We have been pleased to note that some specialist recycling takes place, for example CRL [see the Electrical section] who recycle cellular 'phones, recycle the batteries contained therein.
Lead-acid car batteries are relatively well catered for because they have an obvious scrap value (a substantial amount of lead) and you could possibly collect money by taking them to the scrap metal dealer. Local councils will usually take them for recycling.
Ni-Cd rechargeable batteries contain Cadmium and are increasingly popular. In any piece of equipment they should be easily removable. As long as they're being used they are not dangerous but if they are dumped into landfill they are. Some firms will take them back in part exchange but we have yet to find another convenient and reliable way of disposal for the individual in the UK.
Mercury is used in miniature primary cells ( hearing aids, some cameras). Certain hospitals and jewellers may take these for safe disposal. You may also like to see our note about Mercury under the Fluorescent Tubes heading in this section on Hazardous Waste.