Simple battery question - which one to use?

[9988776655]

My circuit powers a motor which draws about 2A of current out of my 12V lead acid battery.
12V is too much. So I want to change the battery setup.
I want the new battery setup to last as long as possible.
If I continuously use the motor which setup will last the longest?

1) one 6V lithium-manganese photo battery @ 1.5 Ah

or

2) four 1.5V C sized batteries each @ 8.35 Ah connected in series to make 6V

If I use setup 2, will my motor have access to more current?
I know that the motor can only draw current as fast as the chemical reaction takes place in the batteries.

Will setup 2 make my motor go faster than setup 1?

 

[NoTime]

"Ah" refers to the energy content of the battery, not the batterys internal resistance, which is what you need to know to answer your question.

Quiz question. What is the general internal resistance of a LiMg battery vs (guess NiMh) C cell?

 

[pallidin]

The lead acid 12-volt battery your talking about has a much greater current capacity, than either of the others you listed.
You need only 6-volts? There are plenty of 6-volt lead acid batteries available, and not much larger than 4-5 decks of playing cards.

 

[berkeman]

Or you could stay with the 12V lead-acid car battery for the power source, and just use a 12V-to-6V DC-DC converter to make your output for the motor. You could build it yourself (like out of the National Instruments Simple Switcher series, using the Buck Converter configuration), or you can just buy a pre-made unit (I googled 12V to 6V converter, and got lots of hits).

BTW, this is just too funny. One of the first hits on that Google search was for a 12V to 6V converter, that "Allows a 6-volt wiper motor to work with a 12-volt electrical system."

http://www2.cip1.com/ProductDetails.asp?ProductCode=ACC-C10-5754

It's a freaking power resistor! OMG!