Your power supply: battery types & info:

The main choice of laptop batteries -- Lithium ion, Nickel Cadmium or Nickel Metal Hydride.  The right battery power for your make and model can give the best service life with a little proper care.  

The main battery can affect your cycle time, remember.  But with other conditions such as ambient room temperature,  ram versus hard drive actions, associated memory problems and a host of other possibilities there could be an apparent guise of a weakening battery being formed! So you may want to consult a dealer resource before buying.

At the same time, to reduce strain on your power - you may want to consider a desktop charger unit, an  AC adapter and also RAM and CLOCK batteries if needed (not to mention RAM memory)