Just starting to look at GPS for my up coming trip ( Utah Cliff Loop) worried about battery life any good idea?
Most receivers suited for longer trips use two AA cells. Avoid the specialty cycling GPSRs with built-in batteries; they need charging every night. There are just a few practical AA options.
First, among primary (non-rechargeable) cells, alkaline or lithium. (Forget the cheap zinc-carbon cells. They do not last long.) Alkaline cells are cheap, widely available, and power most receivers for 8 to 12 hours. Lithium cells are more expensive, harder to find, about 2/3 the weight, and run 1.5 to 2 times as long.
The only practical secondary (rechargeable) cells are nickel metal hydride (NiMH), which run about as long as the alkaline cells. You can recharge them about 1,000 times with either a plug-in charger or a solar charger. The "regular" variety hold more charge than the precharged variety, although they lose more charge when on the shelf for months: not a problem in this application.
Plug-in chargers are cheap and fast (1 to 2 hours). Solar chargers are more expensive, heavier, and slow. The ones that would fit on a bike need most of a sunny day to charge two AA, and NiMH does not take a complete charge when charged slowly. The solar option might appeal to those who are willing to spend more and work harder to relieve the grid of 0.01 KWH per recharge.
Speaking of the environment, a word about disposal is in order. All of these cells may be safely disposed in the trash. The U.S. government classifies them as non-hazardous waste. However, California and some European countries consider them hazardous. Years ago, alkaline cells contained small amounts of mercury. In my opinion, that and the bad reputation of nickel-cadmium cells, which are indeed hazardous, caused the politicians to ignore the chemists and write the regulations, which you may wish to follow when in those locations.
Planning a five- or six-day ride on Utah Cliffs, if I did not own a charger I would start with two fresh alkalines in my GPSR, two more in my bag, and buy another pair soon after the first two run out. I do own a charger, so would take it and two rechargeable NiMH cells.
Fred