Need Advice On GPS Tracking Unit

How long are you using it? Is it always on? What environmental conditions is it being used in? Do you have a strong signal? Is the backlight on? Are you carrying it on your person? I'm happy to share my opinion but I need more answers first....My gut instinct tells me 60/90 days isn't going to happen of 2 AAA batteries without some sort of external energy running the unit from time to time. I await your answers...

To hell with batteries, think ADAPTER ! An AC or DC adapter @ 1.5 volts should do the trick.......

I never heard of anyone using a GPS for stationary work, so an AC adapter would not work. Most GPS units come with a port for 12 VDC cigarette lighter type adapter, which may be the same as for the AC adapter. Check your GPS manual to be sure if the input is 12VDC. Some DC adapters output a lower voltage, whatever the GPS unit requires, so be careful. Also, the port voltage is not always the same as the voltage of the internal batteries.

Once you have identified the proper voltage, you will need a battery pack matching this voltage. Typical non-rechargeable battery cells (AAA, AA, C, or D) output 1.5 Volts, so you can usually make a pack for voltages which are multiples of that, e.g. 3.0, 4.5, 6.0, etc. Radioshack and other electronics stores (maybe even Wal-mart) sell plastic battery holders which place the cells in series so the voltages add up. Be sure to buy the one which will hold the correct number of cells for the voltage you want.

Depending on your size and weight requirements, you may want to use AA, C, or D-size alkaline cells. Do not use standard or heavy duty types because they will not last as long. Neither will rechargable cells (nickel-cadmium, called Ni-Cad, or the newer Ni-MH cells). If you can recharge the cells at some time during the 90 day period, this could be an option, because they will only hold a charge for 30-60 days. You will have to experiment to determine how much current is being drawn over time and use the storage capacity rating (milliampere-hours or mAH) as a guide only. For example, if you are using a pack that contains cells with a 2400 mAH rating, and your GPS draws 10 mA continous, or 20 mah for only half the time, etc., then your pack should last around 240 hours, or 10 days continuously, before needing a recharge. Also, Ni-Cad and Ni-MH battery cells have only 1.2 V under load (in use), so you will need more cells than an alkaline pack.

For continous usage without recharging, alkaline cells are your best bet. If you have no weight or size restrictions, use D-size cells. C-size are next best, etc. You will then need to connect the wires from the pack to a connector that matches your DC port. These connectors should be available at the same store where you bought the battery holder. If you have an adaptor already (AC or DC) you could cut the connector off of it and splice the two leads together. Be sure you match Negative (-) to Negative and Positive (+) to Positive or you will burn out your GPS.

Another option is to use rechargable Sealed Lead Acid batteries, usually available in 6V or 12V. These are similar to a car battery, only much smaller and lighter, and are sealed so the liquid does not escape. However, they can vent a little gas if overcharged so be careful not to use them in a small airtight space. Some are called "Gell cells" because their electrolyte is gelled, not liquid. A newer type is call AGM, for Absorbed Glass Mat, due to its internal design which allow it to be lighter and more rugged than older types. The smallest SLA batteries are the type used in older camcorders. Larger ones are used for emergency lighting, radio control toy cars, powered kiddie cars and golf carts, electric fences, non-interruptible power units for computers, etc. Some self-contained 12 VDC power units come with a plastic housing, their own recharge circuit, an internal SLA battery, and a cigarette lighter port, so you just plug in your DC adapter.

SLA batteries can usually hold a charge for 60-90 days, depending on their condition (new or old) and how much current is being drained. They will also have a capacity rating in mAH or just AH (1 AH = 1000 mAH). If size and weight is no issue, this may be your best bet.

You didn't say how portable this setup needs to be. Volkswagon ships every car with a solar trickle charger to keep the battery topped up during shipment. These chargers are widely available on sites such as eBay for between $10 and $30. They put out 18 volts at about 170 mA for ~3.2 Watts - way more than your GPS needs. If you're going to be outdoors, you could rig one of these to recharge batteries (you didn't say whether the device needs to be continuously on for 60-90 days, or just "avaiable.") If the size is a problem, smaller chargers are available, like the kind that power small pathway lights.

i read some of the replys,, im not sure if this is a repeat,, but didnt see anything that was same, if you have a back pack type pouch that you can carry, you can buy a smaller 12 v dc battery, like the kind used for emerg, back up lites,, they weigh about 2-3 lbs, and then link it to the 12v car cig adap input,, this would let the unit control the voltage as if it was plugged in to it so you wont have to do any special converting or worry about over voltage,, and would give you many-many times the battery life of a aaa battery,, also,, i have found that the rechargable units for the gps's last much longer than the aaa's, good luck out in the wild!