Use electrical tape to make a little pyramid of batteries. This can be kind of a hassle in the woods, but it is necessary if you want the GPS to run on batteries.
Leave a gap as shown so it fits the battery case.
Put dielectric grease on the battery terminals to prevent sparking under vibration. Use a thin device as a "shoehorn" to compress the spring and slide the taped battery assembly into the battery case. If you use a metal shoehorn, be careful not to short across the battery terminals.
Taping them together, and using dielectric grease are MOST IMPORTANT. If you want to continue to make it more reliable, do this. Put a fluffy peice of tinfoil in your battery cover then press the batteries into the cover and close the latch. The purpose is to measure the amount of clearance in your battery case. Measure the clearance of all 3 batteries.Consider adding layers of tape or foam equal to the clearance.
In this Rino, with batteries as wrapped, the clearance is about 1/16 inch. Use a small peice of foam rubber or other soft stuff to tighten the batteries in the case. If you put too much it will stress the battery cover, and if it pushes too hard on the cover then the water seal won't engage. Use just enough to prevent battery movement. Sometimes there are variations in battery sizes (such as NiCads) so if you use different types of batteries take this into account.
If there are black deposits on the battery terminals, this is carbon buildup caused by sparking under engine vibration. To get any life out of the batteries you must stop the movement of batteries (sparking at the terminal connections).
Inside the battery case, the batteries are suspended between springs.
At certain frequencies (RPMs) the batteries jump around and lift off the
terminals, creating a small spark each time they disconnect. After several
thousand sparkings, a black carbon residue builds up between the contact
and the battery terminal (at 8,000 RPM it can spark 80,000 times in ten
minutes). Even though the batteries are not dead, the electricity can't
get out thus the GPS thinks they're dead and shuts down. You can scrape
the residue off the battery, but the scratches allow more oxygen into
the spark, and removing the plating causes more burning and the oxidation
returns even faster. And it's difficult to clean the contacts anyway,
especially out in the woods. For this reason we advise using external
power right from the start if possible. At the very least tape the batteries
and use dielectric grease (click
here to order
a 1 oz tube) on the terminals to shut out the oxygen which prevents
a burning spark.
"Duracell" batteries appear to have tougher terminals and last
longer under vibration than "Energizers" or other brands. Rechargeable
batteries seem to be tougher than disposables.