If I don't use my MacBook on a battery, does it mean that it will last longer? I heard that when you have normal notebook from HP, Asus, Dell, Acer.... no matter if you use the notebook on battery or not... after 2 or 3 years it will be dead... lasting only like 30 minutes or maybe only 5 minutes... Is it the same with MacBook? I have a MacBook which is 6 years old and it still lasts 4-5 hours.... The Macbook has not been used on battery in those 6 years. ;o)
Apple says that:
Rechargeable batteries have a limited number of charge cycles and may eventually need to be replaced and disposed of.
Naturally, if the battery has not been connected, no charge cycles have passed.
The best way to use your MacBook Pro batteries is to have it plugged in most of the time, and use it unplugged regularly (or daily) to bring from 100% charge to 80% or so. If you don't use it for months, charge it till 50% and store it.
However I strongly advise against Not using your macbook for weeks or months as you will lose some battery capacity. (Charge it and ask a friend to turn it on occasionally.)
The battery is like a thing that needs exercise. Not using it is worse than using it. If you use it daily (like I do) the battery remains excellent. If for three years you use it only occasionally the battery is going to be weaker than if you use it regularly.
I had Sonys and Toshibas and the batteries were weak on those machines (1.5hrs). I had to buy a spare for the Sony (great machine otherwise), but of course, that Toshiba was less costly than a MBP. The newer Apple MacBook Pro batteries are very good. They are rated to retain 80% of the power after 1000 charge/discharge cycles.
Even my previous White MacBook had excellent battery life when I sold it after using it for 3 years. 8 hours if just reading documents, 4.5 hrs Wi-Fi surfing, and I used that thing daily.
My 15.4″ MBP's battery is non removable, and I like it! The newer technology helps retain battery life. I use it daily and the battery life is excellent(mAh reading close to new). The latest OS X (Mavericks) helps save battery usage time. It's a free upgrade and a must. In addition to lasting longer per charge, my MBP also runs cooler!
The short answer to your question is that all batteries will lose capacity with time, regardless of whether the batteries are regularly used/charged or not, and there are some potential dangers in leaving these batteries unused for long.
You can check the state of your unused battery with a free application like coconutBattery:
With coconutBattery you're always aware of your current battery health. It shows you live information about your battery such as how often it was charged and how is the current maximum capacity in relation to the original capacity your battery had when it left the factory.
You are also able to save the current maximum capacity of your battery. So you can see the changes of your battery health over time.
And with the new online service "coconutBattery Online" you can now compare your battery capacity with others.
The statement about the loss of capacity over time applies equally to the Lithium based batteries that are used in MacBooks, other brand laptops, tablets and smartphones. See How to Prolong Lithium-based Batteries.
From Battery University - Is Lithium-ion the Ideal Battery? (emphasis mine):
Aging is a concern with most lithium-ion batteries and many manufacturers remain silent about this issue. Some capacity deterioration is noticeable after one year, whether the battery is in use or not. The battery frequently fails after two or three years. It should be noted that other chemistries also have age-related degenerative effects. This is especially true for nickel-metal-hydride if exposed to high ambient temperatures. At the same time, lithium-ion packs are known to have served for five years in some applications.
Manufacturers are constantly improving lithium-ion. New and enhanced chemical combinations are introduced every six months or so. With such rapid progress, it is difficult to assess how well the revised battery will age.
In the case of MacBook models, Apple recommends storing the batteries at 50% charge if you do not plan to use it for more than six months. Lithium batteries can also go to "sleep" if discharged beyond a set level and/or left unused for a long period of time. In certain cases, it may be dangerous to use such batteries.
For normal usage, Apple recommends that you run the laptop on battery once in a while and also do a full discharge and recharge to calibrate the battery (full discharge/recharge means running it down till the computer automatically goes to sleep or shuts down due to low battery and then recharging it completely to 100% in one go).
For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Apple does not recommend leaving your portable plugged in all the time. An ideal use would be a commuter who uses her notebook on the train, then plugs it in at the office to charge. This keeps the battery juices flowing. If on the other hand, you use a desktop computer at work, and save a notebook for infrequent travel, Apple recommends charging and discharging its battery at least once per month.
See Apple's guide on Notebook batteries for detailed information.
Apple - Lithium-ion Batteries
My answer to "Keeping MacBook Air battery charged at certain level"
My answer to "Unsold iPhones & Battery Life"
The battery wears the least when it is kept at around 40% charge. Unfortunately, for most laptops there is no way to do this, the OS simply doesn't give you that option.
Keeping it plugged in will certainly put wear on the battery, though it is not clear if that will wear it faster than always cycling, charging/discharging.