Is there a switch created that can switch power from one of two 6v batterys to provide constent power?

I am looking to power a digital game camera that runs on a 6v battery. The big square type. I have added a solar charger however if the flash goes off to often in one day the battery is draned at a time when the solar charger isn't effective. My thought was to use two 6v in parallel or use a switch that would switch the power source before the battery is run down letting the other battery to be charged by the solar panel

The end goal would be for the switch to be automatic with out having to be present as the camara is 2 hours away.

The YUKS, is correct about the ASCO automatic transfer switch. They are industrial grade a High $$$$ item.
If you want to transfer the power manually, you only need a DPDT (double pole, double throw) switch rated for the current that your camera uses. You can get these at a Radio shack or an electronics or electrical parts store. wire the switches center poles to the camera and the outside or end poles to the batteries.
Switch to the right for battery A, Switch to the left for Battery B.
If you want they have switches with a center position "OFF" might come in handy for maintenance

Food for thought.

If the pictures are taken by a flash, absolutely continuous power is probably not required, and any single-pole double-throw switch would do; you can get one at the hardware store for less than two bucks. If you want absolutely continuous power, use two single-throw switches, one for each battery; turn the second battery on a moment before turning the first battery off.

Sure, it's actually called an automatic transfer switch. You select it to the power source that will act as the primary, and it compares voltage to a set limit. If voltage drops below the setpoint, it switches over to the backup power source. You'd have to ensure that the solar cell charges both batteries as necessary so the transfer switch has something to transfer to.
These are similar to the switches for portable emergency lighting -- when normal AC power is lost, the light turns on, powered by the battery that is no longer being charged by the wall outlet. I would try looking up ASCO; they make switches small enough that they might work for your application.

You could try just putting the batteries in parallel with diodes on the positive pole of the battery to avoid one battery feeding the other. However, then your charging system becomes a bit more complicated.
If you still want to go the relay route, you could try a latching relay such as the one in the link below. You would only have to energize the coil momentarily to get the relay to switch to the new battery.

if you want a manual switch, you do not need a
DPDT (double pole, double throw) switch, only a
SPDT (single pole, double throw) switch and leave the negatives from both battereis connected to the load always.

What kind of battery are you using? I hope it is rechargable(nicad or preferably NiMH), otherwise the solar panel will not charge it. 2000MaH NIMH AA batteries can be bought for as low as $1 each. 4 of them in a holder makes 6 volts.

I would hook up the Solar panel with a diode to keep it from draining the batteries at night to the battery pack and then connect the batteries to the camera. when the sun is out it will charge the batteries or power your device. you can keep it hooked up always, it can charge and power the device at the same time, you do not need to disconnect it with a switch.

I hope this helps