Using a charger for a battery source

[Scott Berg]

Iota makes good chargers; many can indeed be used as power supplies; recommended...

[MartinF]

This is very risky for any device with electronic components. Battery chargers output un-smoothed rectified AC. For nominal voltage of 16V, peak volts will be 23V. Because of the inductance inherent in the charger's transformer instantaneous peak voltage will be much greater if the output circuit is disconnected or switched off.
M

[john61ct]

MegaWatt power supply, cheaper than Mean Well, don't overload it trying to charge a big empty bank with high acceptance. http://www.ebay.com/itm/180681552153

Mean Wells have overcurrent protection.

[Brewgyver]

Another option for short-duration operation of small DC items is the battery from your cordless tools. Most of us have at least a drill or driver, they're pretty indispensable on a boat. Don't worry if it's 12, 14, or 18 volt, a DC motor will take it.
Example: I have a little Harbor Fright (sic) bilge pump, with a five foot lead terminating with alligator clamps. Have the pump attached to a three foot aluminum pole. I stick the pump down into my dink and pump out the rainwater, just touching the clips to the (18 volt) cordless tool battery contacts. (I wouldn't use the 18 volt to test any 12 volt rated light).