Your voltages are way too low, go have your charging system tested and fix what is wrong so you get back to the 13.6 to 14.4 range.

 

pull into an advance auto or autozone for a free battery, alternator and leak test... theyll monitor the voltage and amps while idle, under various loads, at raised rpm... then idle again at no load to make sure your alternator is kicking on. like mike said, right after startup you should read mid 13's to mid 14's as the alternator recharges what the battery lost starting the engine... it should provide more then enough juice to run the accessories on the truck without tapping the battery and you should see a healthy 12.4-12.6v's or more after until you turn off and back on again.

think volts as water pressure in pipes, amps as the gallons per hour flow rate, and amp/hours posted on the battery as how many gallons of water the battery holds for the system. it takes more pressure to refill the battery after it has leaked out some gallons... and amp hour is how many gallons per hour it can sent out before shes dead. the alternators job is to push water back into the battery at a higher pressure faster then its leaking out under normal drain. starting the car however is like busting open a pipe, you lose lots of water quick, so the pressures on 12v's... but there are are lots of gallons flowing out of a very big pipe in under 5 seconds or whatever it takes to start the motor. then the alternator slowly refills the battery then takes off normal flow to all the fun bits, lights, radio etc. that would slowly drain the battery again if nothing replenished it so you can start your car next time it goes off. just sticking a voltmeter on the battery only shows you that the pressures good on the low pipe, but the waterflows nearly the same whetheres theres a tone of water in the battery or just alittle... until theres almost none left, then all of the sudden theres nearly no pressure.

 

Hey all below is a video I uploaded to Dropbox for you all. It's me meter testing the batteries with the headlights off.

The headlights will come on (although dim), the radio, fans, etc etc all work.

http://db.tt/gU15Pg3j


ps, Sorry about it being sideways----a good neck exercise for you though.

 

If the headlights are really dim - it can be that you just have the city lights working, a small bulb also mounted in the head light fixture, like a parking light. We have had people with both head lights burned out.

Also, it would help to be more accurate if you place the meter selector on the DC scale. On AC it will read something, but depending on internal circuitry of the meter it may not be spot on for DC. From my look at your pix, the meter is reading 27 volts which makes no sense. On the DC scale, the meter should read with the pointer passing thru the word "replace", and use the black scale. You may want to try on another battery. You can haul the bad battery to parts store for testing. You may need a new meter, or you may need to "zero" it by adjusting that big black plastic screw to move the pointer exactly to the zero with leads not connected.