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WHAT IS A BATTERY CHARGER?
Before we can discuss
the battery float charger and its advantages, let's start with the basics.
What is a battery charger? A battery charger is a
device used to put energy into a rechargeable battery by forcing an electric
current through it. The charge current that should be used will depend upon
the technology and capacity of the battery being charged. For example, the
current that should be applied to recharge a 12 volt car battery will be very
different from the current for a mobile phone battery.
On this site, we will discuss
charging of a lead-acid automotive-type battery, An automotive-type battery
refers to a battery used to turn a starter motor,
thereby starting a vehicle (car, truck, motorcycle, tractor,
boat, ATV, personal watercraft, construction
equipment, forklift, etc.). We will also discuss different methods of
charging an automotive-type battery: the
GOOD,
BETTER
and
BEST
way.
WHAT IS A "CONVENTIONAL" BATTERY
CHARGER?
 Before
we begin to explain battery float chargers, we should discuss how a
conventional (simple) battery charger works.
A conventional charger works by supplying a constant DC (direct current) or pulsed DC power source
to a battery being charged. These chargers can supply either a constant
voltage or a constant current to the battery.
 The
conventional battery charger can deliver anywhere from 2 amp to 100 amps (or
more) of DC current to charge an automotive battery. Typically, there
is a selection knob on the charger to change the charge amperage. The
conventional battery charger does not alter its output
based on time or the charge on the battery. Think of it as a "dumb"
charger.
So why even make a conventional battery
charger? If you car battery is almost dead and you
need to start your vehicle in a hurry, nothing beat this type of charger.
This type of charger is common in service stations. Its high output current can dump a lot of current into your battery in only
a short time. But there is a heavy trade-off. The higher the
charge current, the harder the charge is on your battery. And if only
connected to a battery for a short time, your battery will not be properly
or thoroughly charged.
WARNING!
A battery left connected to a *conventional* battery charger for too long
will be weakened or destroyed due to over-charging! This is what some people
refer to as "cooking the battery".
WHAT IS A TRICKLE CHARGER?
 Many
people use the term "trickle charger" to describe any small battery charger.
This is not entirely true. Trickle charging means charging a
battery at a similar rate as the battery self-discharges, thus maintaining a
full capacity battery. Most rechargeable batteries, have a moderate
rate of self-discharge, meaning a battery gradually loses its charge even if
its not used in a device. Care must be taken, however, that if the charger
you use does not have a
battery regulator (circuitry) employed. If the charge rate is greater than the
level of battery self-discharge, then overcharging, possible damage, and/or
battery leakage may
occur.
In other words, a trickle charger will keep dumping
current into a battery no matter whether the
battery is fully charged or not. So if you don't want to ruin your
battery, the charger needs to be connected and
disconnected periodically. Trickle chargers will work to keep the battery
charged, if used once a month or so for a day or two, but the float chargers
can be left connected indefinitely without potential harm to the battery.
WHAT IS A FLOAT CHARGER?
 A float charger
(also called a maintenance charger or smart charger) is similar to a trickle charger in that it will charge a battery at a
similar rate as a battery self-discharges, thus maintaining a full capacity
battery. However, the main difference between a trickle charger and a
float charger is that a float charger has circuitry (electronics) to prevent battery
overcharging. A float charger senses when a battery voltage is at the
appropriate float level and temporarily ceases charging; it maintains the
charge current at zero or a very minimal level until it senses that the
battery output voltage has fallen, and then resumes charging. It is
important to note that the appropriate float voltage varies significantly
with the construction of the battery and the ambient temperature. With the
appropriate voltage for the battery type and with proper temperature
compensation, a float charger may be kept connected indefinitely without
damaging the battery.
How does a battery float charger work?
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