are used instead of SLI batteries for these applications. Traction batteries must be designed with a high ampere-hour capacity. Batteries for electric vehicles are characterized by their relatively high power-to-weight ratio, energy to weight ratio and energy density; smaller, lighter batteries reduce the weight of the vehicle and improve its performance. Compared to liquid fuels, all current battery technologies have much lower specific energy; and this often impacts the maximum all-electric range of the vehicles.

The fact that electric vehicle battery technology has suffered slightly from underinvestment, with more funds targeted towards electric vehicles themselves, we have seen some progress over the last few years. There are a number of different types of electric vehicle batteries available which offer different advantages and disadvantages, although there is no doubt there is a strong movement towards one particular type of electric vehicle battery.

The following chart compares various batteries available for use today and those with a high probability for use in the future. Rough averages are shown here and should be used for general comparisons.  Many of the life cycles numbers are based solely on reasonable estimations.

Type	Energy density	Power density	Cycles	Energy efficiency
Lead-acid	40 W*h/kg	130 W/kg	750	65%
Aluminum-air	200 W*h/kg	150 W/kg		35%
Lithium polymer	100 W*h/kg	100 W/kg	400
Nickel-cadmium	56 W*h/kg	200 W/kg	2.000	65%
Nickel-iron	55 W*h/kg	130 W/kg	1.500	60%
Nickel-metal-hydride	80 W*h/kg	200 W/kg	1.000	90%
Nickel-zinc	80 W*h/kg	150 W/kg	200	65%
Silver-zinc	100 W*h/kg	W/kg	100
Sodium-sulfur	100 W*h/kg	120 W/kg	500	85%
Zinc-air	165 W*h/kg	100 W/kg	240	40%
Zinc-bromine	70 W*h/kg	100 W/kg	500	65%

These are descriptions of the most common types of secondary (rechargeable) batteries for use in electric and hybrid vehicles.

Lead Acid

Usually lead acid battery is 6 volts or 8 volts. A well-develop and tested. It’s widely available and not excessively costly. it is used most in DIY conversions. One of the advantage of lead-acid batteries is their availability,  reliability and affordability.  Lead-acid batteries have a lower energy density than other types. Lesser range and take longer to recharge than some other types of electric car batteries. If you are using lead acid batteries, it is especially important to make sure to recycle your battery. Lead is toxic and leeches into water, or into the air, if incinerated.

• Anode = Pb (lead)
• Electrolyte = 30% H2SO4 (dilute sulfuric acid)
• Cathode = PbO2 (lead dioxide)
• Cell Voltage = 2 volts

Oxidation-reduction Reaction:

• Positive plate (Cathode)
• PbO2 (s) + 4H+ (aq) + SO42- (aq) + 2e- <=> PbSO4 (s) + 2(H2O)
• Negative plate (Anode)
• Pb (s) + SO42- (aq) <=> PbSO4 (s) + 2e-
• Discharging
• PbO2 (s) + Pb (s) + 4H+ (aq) + 2SO42- (aq) <=> 2(PbSO4) (s) + 2(H2O)
• Electrolyte densities at 160 C

There is no doubt that lead acid powered batteries have been around for some time and while they are still very common in electric vehicles there are a number of issues which should lead to the reduction of lead acid batteries in future electric vehicles. Aside from the fact there are recycling and environmental issues with lead acid batteries the number of batteries required to power a modern day electric vehicle can end up being as much as 25% to 50% of the overall vehicles mass. The problem is that only 80% of the power contained within a lead acid battery can be used before the battery is rendered “flat".

Nickel Iron

About 3 hour discharge rate, nickel-iron batteries average 48 watt•hours/kg of energy density.  For a 30 second period the power density rate is 100 watts/kg.  Cycle life of 700 to 1000 are average at 80% depth of discharge.

Nickel Cadmium

Waldmar Jungner invented nickel-cadmium battery, in 1899, offered several advantages over lead acid, but the materials were expensive and the early use was restricted. Developments lagged until 1932 when attempts were made to deposit the active materials inside a porous nickel-plated electrode. Further improvements occurred in 1947 by trying to absorb the gases generated during charge.

For many years, NiCd was the preferred battery choice for two-way radios, emergency medical equipment, professional video cameras and power tools. In the late 1980s, the ultra-high-capacity NiCd rocked the world with capacities that were up to 60 percent higher than the standard NiCd. This was done by packing more active material into the cell, but the gain was met with the side effects of higher internal resistance and shorter cycle.

• Anode = Cadmium
• Cell Voltage = 1.4 volts
• Cathode = Nickel dioxide
• Alkaline (basic) electrolyte
• Anode reaction (oxidation)
• Cd (s) + 2OH- (aq) => Cd(OH)2 (s) + 2e-
• Cathode reaction (reduction)
• NiO2 (s) + 2H2O + 2e- => Ni(OH)2 (s) +2OH- (aq)
• Discharging
• Cd (s) + NiO2 (s) + 2H2O =>  Cd(OH)2 (s) + Ni(OH)2 (s)

 

Nickel metal hydride battery

 

Like lead acid batteries, nickel metal hydride batteries are seen by many as mature technology which are not particularly in sync with the energy/weight ratio requirements of the modern day electric vehicle. While it will last longer than many of the modern day lightweight batteries, although this technology is being improved, there are downsides which include poor efficiency, poor performance in cold weather and potential issues with charging cycles. Research of nickel-metal-hydride started in 1967; however, instabilities with the metal-hydride led scientists to develop the nickel-hydrogen battery (NiH) instead. Today, NiH is mainly used in satellites.

New hydride alloys discovered in the 1980s offered better stability and the development of NiMH advanced in earnest. Today, NiMH provides 40 percent higher specific energy than a standard NiCd, but the decisive advantage is the absence of toxic metals.

The advancements of NiMH are impressive. Since 1991, the specific energy has doubled and the life span extended. The hype of lithium-ion may have dampened the enthusiasm for NiMH a bit but not to the point to turn HEV makers away from this proven technology. Batteries for the electric powertrain in vehicles must meet some of the most demanding challenges, and NiMH has two major advantages over Li-ion here. These are price and safety. Makers of hybrid vehicles claim that NiMH costs one-third of an equivalent Li-ion system, and the relaxation on safety provisions contribute in part to this price reduction..

 

Zebra batteries

Zebra batteries, otherwise known as sodium batteries, use molten chloroaluminate sodium as the electrolyte and again are seen by many as a mature technology although again this particular type of power has played its part in the development of electric vehicles.  A relatively mature technology, the Zebra battery boasts an energy density of 120Wh/kg and reasonable series resistance. Cold weather is not necessarily an issue with this particular type of battery although some of the energy contained within the cell is “wasted” due to the requirement that the electrolyte is heated to 270°C. One of the main issues with any type of all the battery power is the weight and the number of batteries required to power the systems and the services available in the modern-day car.  Zebras can last for a few thousand charge cycles and are nontoxic. The downsides to the Zebra battery include poor power density (<300 W/kg) and the requirement of having to heat the electrolyte to about 270 °C (520 °F), which wastes some energy and presents difficulties in long-term storage of charge.

 

Lithium ion batteries

 

Lithium ion batteries are by far and away the most popular in the UK and worldwide today as they are commonplace in consumer electronics such as laptops and mobile phones. The weight ratio and the number of batteries required compared to the overall weight of the electric vehicle today is very favourable and the fact they will discharge around 80% to 90% of their power before they need to be recharged is also useful. We have seen developments within the lithium ion battery sector and many believe this is where the future of electric vehicle power lies. However, at this point in time there are issues with regards to the short number of cycles which any lithium ion battery can accommodate before it needs to be replaced. This significant reduction in efficiency in a relatively small space of time has led to increased cost issues with regards to the long-term running of any electric vehicle.

Lithium Polymer Battery

Batteries are composed of several identical secondary cells in parallel addition to increase the discharge current capability. The voltage of a Li-poly cell varies from about 2.7 V (discharged) to about 4.23 V (fully charged), and Li-poly cells have to be protected from overcharge by limiting the applied voltage to no more than 4.235 V per cell used in a series combination. Overcharging a Li-poly battery will likely result in explosion and/or fire. During discharge on load, the load has to be removed as soon as the voltage drops below approximately 3.0 V per cell (used in a series combination), or else the battery will subsequently no longer accept a full charge and may experience problems holding voltage under load.

There are currently two commercialized technologies, both lithium-ion-polymer (where "polymer" stands for "polymer electrolyte/separator") cells. These are collectively referred to as "polymer electrolyte batteries".

The battery is constructed as:

* Cathode: LiCoO2 or LiMnO4

* Separator: Conducting polymer electrolyte

* Anode: Li or carbon-Li intercalation compound

Typical reaction:

* Anode: carbon–Lix → C + xLi+ + xe−

* Separator: Li+ conduction

* Cathode: Li1−xCoO2 + xLi+ + xe− → LiCoO2

Charging for Lithium Polymer Battery

LiPoly batteries must be charged carefully. The basic process is to charge at constant current until each cell reaches 4.2 V; the charger must then gradually reduce the charge current while holding the cell voltage at 4.2 V until the charge current has dropped to 10% of the initial charge rate, at which point the battery is considered 100% charged.

Balance charging simply means that the charger monitors the voltage of each cell in a pack and varies the charge on a per-cell basis so that all cells are brought to the same voltage.

The charge should not be terminated on reaching a cell voltage of 4.2 V because the capacity reached at that point is only 70% of full capacity; charging at the reducing current necessary to hold the cell voltage at or very near 4.2 V must be continued until the charge current drops to 10% of the initial charge rate.

Deep Cycle battery types

Flooded

Flooded Deep Cycle batteries are similar to regular car batteries except for the thickness of lead plates which make up the battery. Flooded batteries have most of the same short comings of standard car batteries - such as electrolyte dissipation and hydrogen/oxygen gas venting.

GEL or VRLA (valve regulated lead acid) batteries

GEL battery is a low maintenance VRLA battery with a gelified electrolyte. Unlike a traditional wet-cell lead-acid battery, these batteries may be stored in any position - not necessarily upright. They virtually eliminate the possibility of spillage. Though they are supposed to withstand extreme weather conditions better than wet-cell lead acid batteries, they still need to be run regularly to recharge themselves. The more they are utilized, the better they perform and the more miles the NEV can drive between charges. Without regular use the battery will go bad and need replacing - especially in cold climates.

AGM (Absorbent Glass Mat) batteries

This new improved VRLA battery allows the electrolytes to be absorbed into glass fibers. The plates holding the glass may be flat, or wound (spiral wound). They are an improvement due to their smaller size and unique construction which allows for a purer lead composition - allowing for better conductivity. It may also be charged quicker and have a little better power density overall than the former GEL batteries.

 

All Deep Cycle batteries are rated in Amp-Hours or AH this is a measure of the output current per hour. So for instance a battery rated at 10-AH will supply 10A over 1HR or 1A over 10Hrs. The standard Amp-Hour rating used for a Deep Cycle batteries is the 20 Hour Rate. This rating is based on discharging a 12V battery down to 10.5V over a 20 Hour period and measuring the actual Amp-Hours the battery supplies.

Though all three types of batteries Flooded, Gelled Electrolyte and AGM can be used the latter two offer the best performance and longest battery life. There are many different types of batteries within each category, therefor it is essential to have the proper information on the type of electric vehicle conversion in choosing the best battery for the project.

LiFePO4 Batteries

LiFePO4, lithium iron phosphate as cathode, a kind of advancing technology to change the world.

The safety characteristics inherent to LiFePo4 technology result from the incorporation of phosphates as the cathode material. Phosphates are extremely stable in overcharge or short circuit conditions and have the ability to withstand high temperatures without decomposing. When abuse does occur, phosphates are not prone to thermal runaway and will not burn. As a result, LiFePo4 technology possesses safety characteristics that are fundamentally superior to those of Lithium-ion batteries made with other cathode materials.

LiFePo4 technology does not contain any heavy metals and does not exhibit the "memory effect" of Nickel-Cadmium and Nickel-metal Hydride solutions. LiFePo4 technology demonstrates excellent shelf life, long cycle life and is maintenance free.

Another key benefit of our LiFePo4 technology is its flexibility, both in terms of battery application and cell design. It can be used in wound cylindrical, wound prismatic and polymer battery construction types and manufactured to fit smaller applications.

The advantages of traditional Lithium-ion coupled with the safety features of phosphates, make LiFePo4 technology the Lithium-ion technology for the future. LiFePo4 Lithium-ion technology utilizes natural, phosphate-based material and offers the greatest combination of performance, safety, cost, reliability and environmental characteristics.