Charging a Battery on the Floor or otherwise out of the car...
Steps for Charging Batteries when Battery is outside the vehicle
The checklist for charging a battery when not connected to a load is a bit simpler. There is nothing to ground, nothing else but the battery to be charged. There are 5 points to watch.
Check the polarity on the battery and distinguish the positive terminal and negative terminal. If you are pretty sure after inspecting the case, check the bolt or terminal size. The positive terminal should be a bit larger than the negative. When in doubt, use a volt meter to make sure.
Connect the negative (black) battery charger clamp to the negative battery post
located on battery.
Connect the positive (red) battery charger clamp to the positive battery post located
on the battery.
The red alarm indication light on battery charger will indicate a battery, which is
connected to reverse polarity.
Turn away as you connect the battery charger's AC cord to the wall socket.
It is recommended that you DO NOT face the battery when making the final
connection. If there is a catastrohic failure, you don't want to see ACID flying anyway...
To disconnect charger, disconnect in reverse order from the connecting process.
(Disconnect the positive
battery charger clamp (red) first, then disconnect the negative (black) battery charger clamp next.)
If you can not determine the positive and negative posts with the markings of the battery itself, there is another method. The positive terminal or post should be a bit larger diameter then the negative terminal post. When making this assumption (larger post is positive), do check with a voltmeter prior to hooking up the charger to avoid inverted wiring. Another method for determining positive and negative is the grounded chassis, and general lack of resistance to test with. Since most vehicle applications have the negative battery post connected to the chassis via thick ground straps, "grounding" the frame, there will be very little resistance between the frame and the negative terminal on the battery. Any voltmeter will be able to test for this continuity.
Battery Charger Warnings:
Always read and follow the manufacturer's battery charging instructions prior to
connecting your battery, or trying to charge a battery bank. Do not attempt to charge batteries
in a confined environment. Explosive and hazardous gases are an inherent byproduct of
battery charging, do think ahead. Batteries contain sulphuric acid, and lead, both of which are hazardous material if removed from the battery, or disposed of improperly, do take care to be
environmentally responsible. Batteries are useful, just be safe.