Given equivalent voltages in parallel, the output voltage is equal to the voltage of any
one branch, in this case 11.1V. Power equals Voltage times Current (P = V x I) so increasing current is the
only way to raise power output once voltage has been fixed. Total current equals the sum of the current in
each parallel branch or I
= I1 + I2.
Power equates to run-time, the most sought after battery characteristic. The way to
extend a battery run-time is to add more parallel branches, illustrated by the red "extended life"
cells. Genuine aftermarket extended life batteries will be physically larger than than the original, the
extra cells arranged to protrude outside the notebook case. Usually this is done in an ergonomically
pleasing way. Now Itotal = I1 + I2 + I3.
The extended version of this battery has a 33% greater run-time.
ChemistryBatteries in mobile consumer devices such as
laptops, notebooks, camcorders, cell phones, PDAs, digital cameras, cordless phones, and power tools are
principally made using Nickel Cadmium (NiCad), Nickel Metal Hydride (NiMH) or Lithium Ion
(Li-Ion). Each chemistry is rechargeable but important differences exist.
• NiCad - Oldest rechargeable commercial chemistry, supplanted by NiMH
and Li-Ion due to three main disadvantages. First; NiCad has a lower energy density (energy
output per weight) than NiMH or Li-Ion. Second; NiCad batteries can suffer from the
"Memory Effect". In short, Memory Effect describes a condition where a battery is continually
only partially discharged before re-charging, forgetting the capacity which is still charged. The battery
remains functional, but loses capacity because of the forgotten charge. Finally, NiCad, due to the Cadmium
metal, is not environmentally friendly.
• NiMH - Roughly double the energy density of NiCad, more environmentally
friendly, and much less likely to suffer from the Memory Effect.
• Li-Ion - Defacto standard for mobile power in consumer devices. Better
energy density than NiMH, essentially producing same energy output at 35% less weight. Another huge
advantage is that Li-Ion batteries are immune from the Memory Effect affliction.
Li-Ion is environmentally friendly and can be manufactured at reasonable costs. Virtually all
modern notebook batteries are Li-Ion.
CompatibilityUnlike most computer desktop power
supplies, notebook batteries are not manufactured to a common standard with uniform size, connector
interface, and output. Batteries are manufactured for a specific laptop or laptop series per OEM. Toshiba,
Sony, Compaq, HP, IBM, and Dell each have unique battery designs, even among laptop models. Therefore great
care must be applied when choosing a new battery.
