Connecting to a single battery that is part of a 'bank' will seriously affect the re-charging process and result in overcharging of other cells and their fast demise. Don't do it.

Not a lot of people appreciate that lots of modern electronic equipment will happily accept a DC input directly (I'm talking items that are, or have, SMPS front-ends here so unless you know what you're doing then DON'T just connect a DC supply to equipment without making the necessary checks).

Here in the UK a DC supply will power laptops, PC's, TV's etc (consider that the standard AC supply (240V) is rectified before being 'chopped' in most SMPS units then doing the rectification BEFORE it enters the SMPS has no appreciable effect). You can probably get away with 120V to 350V DC since the SMPS's I'm 'looking at' accept anywhere from 90-260VAC input.

NOT FOR THE 'EXPERIMENTER' - KNOW WHAT YOU'RE DOING BEFORE TRYING THIS!!!!!