The Natural Philosopher wrote:
On Wed, 04 Jan 2006 15:35:15 +0000, Steve Firth wrote:
[snip]
It's because lead acid batteries don't need complex charge controllers,
work across a wide range of environmental temperatures and provide huge
cranking currents time after time. They are big, rough and tough and
also extremely efficient compared to any of the alternatives around.
Where they fail is on charge per kg which is where Lithium based
batterys win. Where Lithium batteries fail is on charge/discharge
cycles, efficiency and the need for complex charge cycles and careful
management of discharge.

Actually, most of that is utter tosh.
[snip]

Tosh and piffle yourself:

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Battery Thermal Management in EVs and HEVs:
Issues and Solutions
Ahmad A. Pesaran
National Renewable Energy Laboratory
Advanced Automotive Battery Conference
Las Vegas, Nevada
February 6-8, 2001

"The need for battery thermal management for ambient temperature
batteries such as valve regulated lead acid (VRLA), nickel metal hydride
(NiMH), and lithium ion (Li-Ion) was not obvious initially, however, EV
and HEV battery and vehicle manufacturers have come to realize such a need."

"Since Li Ion batteries can deliver much more power and thus more heat
for the same volume than either VRLA or NiMH, heat removal needs to be
efficient. Thermal management also depends on the type of vehicle and
where the pack will be located. For EV and series HEV, the pack is
generally large and its thermal management system may need to be more
elaborate, possibly incorporating liquid cooling"

"Li Ion batteries also need a good thermal management system because of
safety and low temperature performance concerns."

"Li-Ion generates more heat in a smaller volume and is more sensitive to
extreme cold and hot, so also need (sic) a complete battery management
system"

The paper notes that an 80-50% discharge of a test Li Ion traction
battery cell produced 2W of heat per AH of cell capacity compared to
1W/AH for Lead Acid, also that the heat evolved by Li Ion batteries on
discharge increases as ambient temperature is reduced.

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http://www.powerstream.com/li.htm

... a charge timer should be included for safety.

The charge cannot be terminated on a voltage. The capacity reached at
4.2 Volts per cell is only 40 to 70% of full capacity. For this reason
you need to continue to charge until the current drops, and to terminate
on the low current.

It is important to note that trickle charging is not acceptable for
lithium batteries. The Li-ion chemistry cannot accept an overcharge
without causing damage to the cell, possibly plating out lithium metal
and becoming hazardous.

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http://www.batteryuniversity.com/partone-5.htm

The lithium-ion battery

...

Despite its overall advantages, lithium-ion has its drawbacks. It is
fragile and requires a protection circuit to maintain safe operation.
Built into each pack, the protection circuit limits the peak voltage of
each cell during charge and prevents the cell voltage from dropping too
low on discharge. In addition, the cell temperature is monitored to
prevent temperature extremes. The maximum charge and discharge current
on most packs are is limited to between 1C and 2C. With these
precautions in place, the possibility of metallic lithium plating
occurring due to overcharge is virtually eliminated.

Aging is a concern with most lithium-ion batteries and many
manufacturers remain silent about this issue. Some capacity
deterioration is noticeable after one year, whether the battery is in
use or not. The battery frequently fails after two or three years.

The lithium Polymer battery

Lower energy density and decreased cycle count compared to lithium-ion.
Expensive to manufacture.
No standard sizes. Most cells are produced for high volume consumer markets.
Higher cost-to-energy ratio than lithium-ion

------------
http://www.tmcnet.com/usubmit/2004/Oct/1080857.htm

Charging Lithium-based batteries requires different technologies from
those used for other cell chemistries. Attempting to charge
Lithium-based batteries beyond 4.2 Volts per cell permanently damages
the battery and may result in the battery exploding. Over discharging
Lithium-based batteries also results in irreversible changes to the
batteries. For this reason, manufacturers incorporate
semiconductor-based protection circuitry in the Lithium battery pack to
prevent this from happening. In addition, Lithium-based batteries must
be limited in the amount of current they supply; significant
over-current discharge can cause this type of battery to explode.
...

This relatively long charging cycle compared to that of other battery
chemistries is one of the less desirable characteristics of
Lithium-based batteries. Another undesirable characteristic is “capacity
fade”. Each time a Lithium-based battery is charged it loses a little of
its storage capacity. All battery chemistries exhibit some capacity
fade, however, Lithium-based batteries fade more rapidly than Ni-Cd or
Ni-MH batteries. The battery loses a little capacity each time it is
charged. Cell resistance increases with each charge cycle until the
battery is no longer usable. It appears as if the act of charging the
battery damages it, almost as if the size of the battery plates
decreases with each charging cycle.

------------
http://www.batteryuniversity.com/parttwo-34.htm

You will see that LiIon batteries only hold a charge over a long period
if charged to 40% capacity. Charge to 100% and the loss of charge is
rapid, especially at the temperatures to be experienced inside a car.