(I have not read everything in this thread.)

You can buy a lighter socket with fly leads from Jaycar and crimp terminals for an SLA to it.  Then use a USB lighter plug adapter.  But yes, most cheap ones (and some expensive retail ones) are crap.  It is not about the components they use, but rather how it is assembled and the amount of heatsinking provided and the wire thickness.

There is usually a fuse inside lighter plugs, often you unscrew the tip of the plug where the positive contact is.  I've seen it inside lighter plug USB adapters also, but only in the full sized adapters not the miniature ones.  The miniature ones usually have a self resetting thermal fuse (or supposed to).

And you know for Apple products you can't use the same adapter as for other products.  Apple requires a specific voltage divider on the USB data lines before it will go to max charging current.  The newer iPads will actually run flat while connected to an adapter that does not have the resistors to identify it.  Virtually all other brands of products you just have to short the data lines out (which is the official USB battery charging spec).  If it was not against the forum usage agreement, then I would call apple something else (I design product that has to also work with Apple, don't get me started).