Cordless drills provide many benefits over normal drills. There is no need for that big pile of mangled wires in the back of your truck. They are flexible, portable, and are the new industry standard. They used to be very expensive, but today everything is wireless so it is a must if you are a carpenter or handyman.
These large battery packs take up a lot of room and are pretty heavy, which adversely affects the fuel economy and the storage space in most hybrid cars. These batteries get their power from regenerative braking and/or from the gas engine. Also, they are very expensive, costing thousands of dollars to replace. Which is why they are guaranteed for the life of the car (read you warranty, some states make automakers guarantee the battery for 100,000 miles).
True that they contain the same eddy stock amount and they can last the same amount of minutes but sometimes the batteries of one model does not fit the model of another.
Much of the response to the threat of Giardia is overkill. A favorite scholarly article on Giardia was written by Robert L. Rockwell, PhD. It's titled, Giardia Lamblia and Giardiasis, With Particular Attention to the Sierra Nevada. Bob Rockwell is an active mountaineer who made his first trip into the Sierra Nevada in 1952 to climb Mt. Whitney, and he repeats this climb several times annually. He has a bachelor's degree in Physics from UC-Berkeley, and a PhD in Aeronautical and Astronautical Engineering (Biomechanics) from Stanford.
Another thing to remember is not to store those batteries in the charger as well. This will draw energy away too, and cause your battery to die off sooner than you expect. Keep it away from high heat or extreme coldness. Heat tends to cause damage to your Lithium battery stocks while exposing it to low temperatures over a period of time will draw its charging capacity.
What are you going to be using the drill for? Let's say that you are planning on building some light furniture and maybe will use the drill on weekends mostly. You probably don't need a super powerful drill with the most expensive battery technology. You could probably get by with a 12 volt drill, no need for hammering action, and you could probably do fine with a NiCad battery as opposed to Lithium Ion. Sure, a Lithium mines Ontario Ion battery would be really nice, and would charge faster, but if you aren't planning on using the drill for continuous hours at a time you could save a few bucks in this department.
Most automakers would like to see Lithium-Ion battery packs (you probably have a Li-Ion battery in your cell phone) which can store more energy. But as of right now, they are still too volatile/unreliable when placed in large packs for major carmakers to use. But that should be changing in the next few years. Both GM (with their Plug-In Saturn Vue) and Toyota (next generation Prius/ Hybrid Systems) believe the next generation of hybrids will come with Li-Ion battery packs.
Another one of the best drills out there is the Panasonic EY7540LN2L model. It makes fastening jobs a cinch. It is lightweight, and ergonomic. It is extremely easy on the wrist and hands, so it is comfortable to use. It has long lasting lithium batteries for longer jobs. It is an impact driver, and is definitely versatile. It costs more than the other two drills, but it is still one of the best. Overall, any of the drills mentioned above would be a great cordless drill to own.