Trickle charge is what it says. The charger just trickles a very small charge, 12 volts or so but with a very small current (amps) into your battery. Say your battery charger at full charge puts out say...4 amps, on trickle it may only put out say 800 milliamps. Thats .8 of an amp. The charger only puts out what is required to charge the battery. This is only an example and depends on the charger of course. A trickle is desinged to keep your battery topped up.
Most domestic chargers work on whats called "peak detection" which means the charger recognises when the battery is getting full (peaking) and lowers the current (amps) accordingly until it's charged and then goes into trickle mode. Some more expensive chargers have a two or three stage charge mode as well as a normal mode, but these are mainly used on deep cycle batteries though. There are chargers out there that do everything except make a cappucino and these can be very expensive and not usually used for domestic purposes. I used to use one of thoses little common black wall chargers that you get with portable devices such as portable DVD players and the like on my Harley to keep it charged. It put out about 500 Milliamps (.5 Amps) @ 12 Volts and that kept the battery topped up. There is no reason why you couldn't use one of those on your car.There is no way a trickle charge will charge a flat battery because it just can't put out the current that the battery needs. It would be like eating one sultana every hour when you are hungry, it's just not enough. Disconnect the battery as mentioned above because even with the car turned off the car always finds ways of using your battery and a trickle charge wont do much with it connected. A trick I was told is that when you take your battery out of your car to charge it, raise it of the ground especially if you have concrete or put say, some foam or some type of insulation or even a thick layer of news paper under your battery. It will charge quicker and better because they dont like the cold. Ever noticed when you charge a couple of double A batteries they get warm...well batteries charge with heat in conjunction with the charger if you know what I mean. So keep the little fella warm. Oh, don't top up your battery with water or whatever before you charge it except if the water is below the plates because the charging will more than likely cause it to over flow. Top it up after the charge. Some one did that at my work with an electric forklift and let's just say we had an extremely clean concrete floor the next morning. Get this. A friend of mine once charged a lithium watch battery in his oven for a few minutes and it worked!!! if only for a few days. DONT EVER try to charge any battery like that, because it will probably explode. But you can see in that instance how heat has a big part in charging a battery. Oh and buy the way, don't use your charger to jump start your car, be patient and wait 'till its charged. The charger wont like that because the starter is trying to suck a couple of hundred amps out of something thats only puting out 4 or 5. Guess it would be like trying to suck a golf ball through 10 feet of garden hose. Anyway I hope this has answered any questions that you may or may not have and any that you were or were not thinking about.
