-- Battery Size --

For cordless tools, the amount of available power is determined by battery voltage: the larger the voltage, the more power and torque the tool will have available. While having more torque and power sounds like like something you want, there are trade-offs to be had. Higher voltage cordless tools are heavier and more expensive than their low voltage competitors.

Here's an example to illustrate the point. A typical 9.6 Volt cordless drill will typically weigh about 3-1/2 pounds and cost in the range of $35 - $150. By comparison, a 19.2 Volt cordless drill can weigh up to 10 pounds and cost anywhere from $125 - $300. If you really need the power of a 19.2 Volt cordless drill, then the added cost will be money well spent. But if you are using your cordless drill to occasionally drive screws in your home, a 19.2 Volt cordless drill is probably not worth it since it is harder to use (since it is heavy) and money not well spent. If you really do not need the extra power, a cheaper, light-weight cordless drill may suit your needs better.

-- Battery Type --

Two types of batteries are available for cordless tools: Lithium Ion (Li-Ion) and Nickel Metal Hydride (NiMH). Whatever tool you decide to get, do not get a cordless tool that includes NiMH batteries. Yes, it may be cheaper, but it is cheaper for a reason. NiMH batteries have issues with memory problems (the batteries need to be completely discharged prior to being recharged or they lose charge capacity), they do not last for as many charge cycles (the batteries die sooner), and the batteries have lower power than Li-Ion batteries of the equivalent voltage.

-- Number of Batteries --

Another issue to consider when buying a cordless tool is the number of batteries that come with the tool. If you plan on using your tool often or for extended periods of time, you'll want to only consider tools that come with two batteries. There is nothing worse than having your battery die and having to wait a couple of hours for the battery to charge before you can get back to what you were doing. When you are purchasing a tool, check that it comes with two batteries. If it does not, find out the cost of an additional battery and include that when you are comparing costs between tools.

--Charging Your Batteries--

Many higher-end cordless tools come with advanced chargers which allow the battery to be charged very quickly; on the order of fifteen minutes. For comparison, a standard charger can take up to 3 hours to charge a battery. If the battery charge time is going to be an issue for you, look into the charging options that are available before you buy a cordless tool.

-- Tool and Battery Storage --

Even when your cordless tool is off, it will use a small amount of power from the battery. While the amount of energy being drawn is slight, it can add up over the course of days, weeks, or months. To keep this from occurring when you put away your cordless tools, make sure to remove the battery; this will help ensure that it is charged when you go to use it. Do not store your battery in the charger. While there are some battery chargers that claim to be "smart" about this, but as a rule keeping your cordless tool batteries in the charger will lead to them dying sooner than if you do not. When storing cordless tool batteries avoid cold and/or heat. Cold weather will not ruin your battery long-term, but it will reduce the amount of power available when the battery is being used. High heat can permanently destroy the batteries of your cordless tools. Avoid high heat, and never charge your batteries in an area that is extremely hot, this can permanently ruin the battery.

-- Pick a Brand --

One possible way to avoid problems with the availability of charged batteries is to pick a brand and a battery size and stick with it. If you consistently purchase the same battery size and brand of tool when buying lights, screwdrivers, saws, drills, etc, you will be able to swap batteries and chargers across all of your tools. This will greatly increase the number of available batteries and it ensures that you will never run out of charged batteries.