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Deep Cycle Batteries
Deep cycle batteries are the preferred choice for applications where you need to use ALL the charge in the battery without damaging it. Imagine a golf cart and being able to drive it all 18 holes including finding all the balls your slice lost. Much like the golf cart, the AGI electrical resistivity instruments (SuperSting, MiniSting) require a power source that can be recharged and reliably supplies up to 20A current at more than 12.1V (why 12.1V?)
Car batteries are used to start a vehicle's motor. Starting a vehicle requires an enormous amount of electric charge in a very short period like when you turn the ignition for a couple of seconds to start your car. After this point, the engine is running which turn the alternator which recharges your car battery.
The AGI electrical resistivity instruments (SuperSting, MiniSting) can operate on either type of battery. However, a car battery receive damage after a couple of deep discharges. It's expensive to replace batteries every couple of surveys and even more costly to mobilize to a site only to find out that your car batteries are malfunctioning. Do Not Use Car Batteries!!!
Have you noticed that a 12V battery when fully charged is around 13V? Under a load, meaning that we use some the batteries electric charge to do something like run our instrument or power the light of our car, the voltage will drop significantly of the discharge period of the battery.
Discharge period: The length of time a battery can supply its rated current output. The unit is "Amp Hour." If you look at a rechargeable AA battery, it may say something like 1500mA which means that it can output continuously 1.5Amp for one hour at 1.2V.
A simplified example: How long will my two car headlights run if I forgot them ON overnight?
Let's assume that your vehicle has one 12V battery (OK you diesel truck people stay out of this. We know you have two batteries) and each lamp bulb is rated at 50 watts each. Your car has two headlights. The 12V battery has a 60AHr (said "amp hour") rating.
Summary: The car headlamps will together produce 50 Watt + 50 Watt = 100 Watt at ~12V.
Power = Voltage * Current
100 Watt = 12 V * Current
The amount of current is then = 100/12 ~9.2A. When the headlights are ON, they will draw around 9.2 Amp from your battery at 12V.
Our battery is rated at 60AHr which means that it can supply 60A for one hour BUT our headlights don't need 60 Amp, they only need 9.2 Amp.
Let's calculate how long they will last:
60 Amp Hour/9.2 Amp ~ 6.5 hours
How does this have anything to do with the SuperSting Electrical Resistivity Imaging System?
The AGI SuperSting has a rating of 200 Watt output. Super secret hint: it actually will output more than its published rating. To output current it must also consume some electric charge (current) in doing so. This is referred to its efficiency. If we neglect its inefficiency (transmitters just like people are not perfect) assuming that the SuperSting is running continuously, it could draw up to 20 Amp (it's rated at 200 Watt output) which is twice the power of the headlights in the above example. It's reasonable to draw the conclusion that it will run for half the time the headlights will. That is just a little more than 3 hours.
