BY JONATHAN MELBY

Like most portable electronics, some automotive navigation systems have built-in rechargeable batteries (usually nickel-metal hydride (NiMH) or lithium-ion (Li-Ion)). Batteries that are well cared for will have a longer productive life span and need to be replaced less frequently.

In researching for this article, I looked for sources that appeared to understand battery chemistry and test their hypotheses. Here are some key findings from my research:

Avoid High Temperatures

Tests show that keeping a battery at 115°F will reduce the cycle life by up to 60%. Higher temperatures do even more damage.

• Your GPS battery will last longer if you avoid leaving it in a vehicle on hot sunny days.

"Shallow" Discharge / Recharge Cycles are Best

Tests show that lithium-ion batteries that are only depleted by about 25 to 30 percent before recharging can be expected to take 5 to 6 times as many charge cycles as a battery that's always discharged to maximum design specifications.

• Charge your GPS battery after each use (unless you're planning to store it for a while).

Store Batteries in a Partly Charged State

I didn't find any specific test results for this claim, but otherwise reputable sources suggest that rechargeable batteries should *not* be stored in a fully charged condition. Nor should they be allowed to discharge beyond their design specifications.

Most sources suggested storing batteries with a 40% to 50% charge.