You can look in the manual. However, most main laptop batteries, that power the unit when not on AC power, are in a bay and has a clip that holds the battery in place. It typically slides to disengage and then the battery usually slides out.
The four major manufacturer's of laptops are Toshiba, IBM, Dell and HP/Compaq. They have all been manufacturing laptops for many years. All four make quality products. Toshiba and IBM (now Lenovo) tend to make the most reliable products. Both focus on the corporate marketplace, as do HP and Dell. These companies often farm out the manufacture and sometimes the design of their products to other companies. Many of the components are made by third party companies, like the CPU, memory, hard drives, the keyboards, the LCD displays and most of the components.
Any of these manufacturers would make a good choice. Many older laptops that you find from the companies that sell refurbished laptops come from leasing companies and corporations.
A key is to check the warranty offered by the refurbishing company. Call their customer support and find out how responsive they are. Review the warranty and note that most do not warranty the battery. Check battery sites to see how much a new battery costs.
Decide critical features. Word processing requires minimal CPU power, as you can't type faster than a very old Pentium CPU. In the case of sending and receiving e-mail the CPU does not matter and even a 56K modem is fine. In the case of browsing the Web at least 128MB RAM and a decent connection speed, like DSL or Cable require an Ethernet connection. These are easy to add to old laptops.
Decide on your budget and type used laptops into Google and check out the companies you find there. At the top of the list you will find www.usedlaptops.com (creator of this blog), but be sure to check a few others before making your decision and call a few of the companies before deciding.
Older laptops are perfectly cabable of supporting local area wireless capability. Pentium 2 and later laptops include PCMCIA card slots. These are slots that are slightly larger than a credit card and standard on laptops. Manufacturers make wireless cards that will slide into these slots and provide software on CD and/or downloadable that will allow you to connect to local area wireless networks. If you want to do this in your home and you have DSL or a cable modem you will need a wireless router to transmit the signal to these wireless cards in the laptop.
Some cautions: You should make sure that you have the latest version of software and make sure your firewall is turned on and configured correctly. Snoopers or worse yet criminal might get access to your files. If you are using your laptop in a public wifi site make sure it is a legitimate location, as they most like have their own security in place. When using your e-mail instead of sending and receiving it from a program use an web based provider like GMail or Yahoo Mail to send and receive messges, as they have security that protects data transmissions.