Charger for 12V battery & calculation of watt

Forgot to ask one last question:

http://www.amazon.com/Roadpro-12V-Hot-Pot-oz/dp/B000667QL4/ref=sr_1_1?ie=UTF8&qid=1387987622&sr=8-1&keywords=battery+powered+kettle
  Can I just cut off the car lighter charger of the above hot pot & then
  use the Rayovac battery (with crocodile clips) to charge/heat up the
  hot pot?

http://www.amazon.com/CTEK-Multi-12-Volt-Battery-Charger/dp/B000FQBWCY

Would the above charger work in my country as the input power in
my country is 230-240 Volt.

I'm looking at the charger below but it did not specify the input voltage:
http://www.amazon.com/Black-Decker-BM3B-Battery-Maintainer/dp/B0051D3MP6/ref=sr_1_3?ie=UTF8&qid=1388073211&sr=8-3&keywords=12V+charger

The model below specifically mentions it could support 240V input
but it's a costlier charger:
http://www.amazon.com/Battery-Tender-022-0150-DL-WH-Waterproof-Charger/dp/B000CITKCE/

We ever sparked a mini fire/blaze when using fossil fuel
thus battery is preferred.

Wife is afraid of fossil/propane/kerosene fuel for fear of catching
fire or explosion

serialband brought up some interesting facts about the warmer.  How often do you intend to use it? Do you realize, if you don;t insulate the alligator clops and leaders very well, the assembly could short out and provide a few minutes of fireworks?

So can I say 12V 7Amp battery would last 1 charge only to
boil 20 oz of water?

Thank TG, I'm aware of the sparks if the alligator clips touches
each other : have seen those car batteries clips touching each
other causing sparks.

This question is outside of the norm for EE.  Is this an assignment you are working on or real life experience? Tell us what made you decide to ask this question....

@sunhux - Thanks, and I was happy to help you with this.


... Thinkpads_User