Q:

Are sealed lead acid batteries water-resistant?

I am going on a climbing trip in the Canadian Rockies for 20 days starting this weekend.  I am bringing a 12volt 7Ah SLA battery that I am going to use to charge my GPS, iPod, Camera, and Sat Phone.  
I ordered this Yuasa battery.  Will using this in a wet environment, and possibly getting rained on be bad for the cell?  Will the water be able to get inside?  I figured if the Lead Acid and HCl can't get out, then water can't get in.  Is that true?
Also, I know that cold weather makes the life of Alkaline's and even Li batteries shorter, does the cold have a negative effect on Lead Acid batteries?

A:

Water shouldn't be able to get inside sealed lead-acid cells.  The terminals are not environmentally sealed, though.  If you backpack gets soaked, they battery could discharge through the wet cloth.
Cold increases the internal resistance of the batteries.  As a result, you lose more energy on the internal resistance.  You will get less charge back from the battery.  Max output current also decreases*.  At 00C, you should still be able to get few amperes necessary for charging your gear.

(source of image)
* BTW, vehicle starter batteries are rated for Cold Cranking Amperes. So, they are rated for the worst case.

A:

The battery will be safe to operate in wet conditions provided it is genuine. I'm not aware whether battery counterfeiting is an issue in the US but note that some low grade "sealed" batteries are not sealed. Yuasa are competent and reputable and their claims can generally be trusted.
A genuine Yuasa NP7-12 battery datasheet here is designed to be operated in any orientation and is "perfectly sealed" according to Yuasa. Operation underwater would probably be "unwise" - not liable to be a problem in your case.
There is an overpressure venting system which operates only when the battery generates excess pressure due to Hydrogen generation - which will not happen under normal operation due to designed recombination of gas.
The Genesis label on the battery pictured  is due to rebranding of Yuasa (or Enersys) batteries in the US by Genesis.
Genesis say (from here)

The NP Genesis batteries is used in general electronics and comes in many different sizes for various applications. The construction of the NP is the sealed technology, which means it is guaranteed to be leak proof regardless of the position in which the battery is installed. In addition, the batteries offer the electrolyte suspension system, which includes high porosity and fiber materials that are designed to absorb the electrolyte. The NP batteries have no gel or any other type of contaminants that are used.
In addition, the NP Genesis batteries offer a built-in design, which controls the gas generation and includes a recombination that is more than 99 percent during the float usage. One of the best features of the NP is they are maintenance free. There is no need to add water or check the electrolyte levels. It is truly an install and forget it type of battery.

Here is a superb Yuasa NP series sealed lead acid battery application manual which provides much detail on the care and feeding of your battery.

