why is their need to drain a battery before charging?

Answer 1

car battery ?? dont do it this will shorten the life if not kill it all together that is only for rechargeable ni cad ones

Answer 2

You didn't specify what type of battery or what device it would be used for.

Generally, batteries are often shipped only half charged with a manufacturer note to fully charge it before use.

A common belief for recharging NiCad batteries (take notebook computer batteries for example) is that it is best to regularly drain a battery then fully charge it.

It is believed it is not good to keep a laptop plugged into the AC power source continuously if you have a battery in it. Especially since the recent laptop battery recalls called attention to a few instances when a defective laptop battery overheated/leaked/caught fire.

Best advice: follow the instructions of each manufacturer and device exactly. That way, if something goes wrong, a replacement may be covered under warranty.

Good luck.

Answer 3

If you are talking about draining the electrolyte out of the battery before charging, THIS IS WRONG and DANGEROUS.
If you are talking about running a car battery down to no charge left in it before you charge it, this does not typically need to be done. There are some rechargeable batteries used in various cordless devices that require running the charge down before recharging. This is done because the battery can develop a "memory" of how much you use the device before charging, and then it will only hold that amount of charge (say you typically use it for 3 minutes, then stick it back on the charger. The battery will soon want to run at full output for only the 3 minutes if it's not run to no charge before recharging). Typical examples are camcorders, cordless hand vacuums, etc.
This does not happen with your car battery.

Answer 4

You don't mention what type of battery you are talking about. A car battery should not need charging unless it has been drained due to the lights being left on or a bad charging system, so I'll assume you are referring to something else, like a cell phone battery.

NiCd Ni-Cd batteries are the least expensive and are commonly used for cell phones. The problem with Ni-Cd batteries is that they are very prone to voltage depression, otherwise known as "memory effect". This occurs when recharging a battery before it is fully discharged causes the battery to "remember" its previous partial charge level and not charge to full capacity. To increase life please remember to fully discharge the phone before charging.
NiMH Ni-MH batteries are a superior replacement for Ni-Cd batteries because they are available in higher capacities and are virtually memory-free. That means you can charge the battery when it is convenient for you, not when the battery is "ready".
LiIon Li-ion batteries are the best rechargable batteries available. They offer long life and high capacity in slim, lightweight batteries that are also memory-free. Li-ion batteries are batteries available for many premium cellular phones.

Answer 5

Because you can really mess up the battery! It will die out when it gets back to level it started out on, thinking that level is the end and need to be charged again! Phones are funny that way but hey everything has a mind of its own, just like the dirt in my back yard!!!