I'd like to have a bigger battery power my arduino project. Ideally it would run for several days (or longer) without charging. There is a large power requirement with motors (and motion sensors), so I was thinking of using something like motorcycle batteries.
I'm very new to electronics (not programming), and I'd like to know what is involved with this. Is it simply a matter of a voltage divider with resistors or something else?
I was also considering setting up two or three batteries in parallel, if that's possible.
Realistic or silly? 
Realistic - if running arduino from 12V it will just the current it needs, let your motors run direct from the battery, or give them their own switching regulator, see www.pololu.com for examples. Can run the arduino from switching step down regulator as well for more efficient use of your power.
When I search for "down regulator" on that site I get about 24 pages of hits. Could you provide a more specific example? Something I connect between the batteries and the arduino power input? Can you give a product link? Many thanks.
www.pololu.com, click the Regulators on the left side, will bring up a page of devices.
Browse thru & find something that will the current needed for your unspecified motors.
If you can't find your current size, at least you'll know what you are searching for.
You can get a ready built regulator here:-
Unless one lives in the US, then that's a bit inconvenient!
Hard to tell with the geographically challenged newbies ...
I found a few on Pololu that should do. Before I buy them, though, I want to make sure I can make everything work as I expect.