Scott O'Connell reports that a fresh set of Lithium batteries lasts about 31 hours in his G-12xl.  These batteries cost about $10 for a set of 4.

Most users get about 20 to 24 hours on a set of quality Alkaline batteries.  Thus,  it is normally much more economical to use Alkaline batteries than Lithium batteries unless low temperature operation is important.  Sony, Kirkland, or Toshiba batteries are available in packages of 40 in the Atlanta area for about $9.  We find that the typical Alkaline battery has a capacity of 1800mah at the currents required by GPS receivers.

NiCad batteries typically have about 1/4 to 1/3 the life of Alkaline batteries in GPS receivers.  On the other hand,  they can be recharged about 500 times and so are an economical choice if the inconvenience of a recharge or battery exchange every 7 hours or so (in a G-12xl ver 4) is not a problem.

Nickel Metal-Hydride (NiMH) offer increased capacity over the NiCad batteries without the 'memory' problem.  These come in 1200, 1600, and 1800mah capacity where the NiCads are generally 875mah.  (A Street Pilot will log 6 hrs of continuous use on a set of 1200mah batteries before shutdown.)

We ran down three sets of AA batteries in a Garmin G-III+ with Power Saver and Simulator OFF.  With the alkalines as a standard, this is what we got:

                                   TIME   COMPARISON TO ALKALINE
Costco Alkalines:          20:15            100%
Radio Shack NiMH 1600mah:  16:15             80%
Radio Shack NiMH 1200mah:  12:55             64%

Starting NiMH voltage was 5.7vdc and ending voltage was 4.2vdc.  The starting current was 82ma.

Alkaline rechargeable batteries are another option.  They usually last about 1/2 to 2/3 as long as regular alkaline batteries and are rechargeable about 25 times before the life time is cut to about half of the original.

Joe Mehaffey and Jack Yeazel