During the last decade, cordless tools have expanded in voltage and applications to become primary tools on residential and commercial job sites. Recently, lithium ion battery technology has been introduced into power tools. But what is the benefit of lithium ion?
For a given voltage, a lithium ion battery is smaller in size and lighter in weight than a nickel cadmium (NiCd) or nickel metal hydride (NiMH) battery. In addition, lithium ion has virtually no self-discharge. This allows a lithium ion battery to be stored for months without losing charge. The battery chemistries can be compared as follows:
Lithium ion has an ergonomic advantage over the other battery chemistries. But what about performance and durability?
Rule 1: Lithium ion does not mean more power
As power increases, a tool can perform more difficult applications and do the applications faster. Power is determined by the voltage of the battery and the efficient design of the motor, transmission and mechanism. Increasing voltage or efficiency increases power. Note that battery chemistry does not influence power. An 18V lithium ion battery has the same potential to deliver power as an 18V NiCd battery because they are the same voltage.
However, the ergonomic advantage of lithium ion batteries allows manufacturers to make higher voltage tools-and, thus, more power-without increasing weight.
Rule 2: Lithium ion does not mean more run time
The run time (or number of holes drilled on a single battery charge) is determined by three factors:
1. Battery voltage
2. Battery capacity (amp-hour)
3. Efficiency of tool design
Increasing voltage, amp-hour or tool efficiency improves run time. NiCd and NiMH batteries range in capacity from 1.3Ah to 3.0Ah. In comparison, lithium ion batteries range from 1.1Ah to 3.0Ah.
Remember, amp-hour is only one factor in run time, just as the size of the gas tank is only one factor in how far a vehicle can drive on a tank of gas. The best measure of run time is how many holes are drilled or how many boards cut on a single battery charge. Applications per battery charge factor in voltage, capacity and the efficiency of the tool.
Rule 3: Lithium ion has various formulas
There are hundreds of formulas of lithium ion, each with various features and benefits. Some formulas provide far more positive benefits than others. When purchasing a tool, it is important to understand the performance and durability of the specific product you are considering. For example, consider how many holes you can drill per charge or how many recharges you can get during the battery's life.
It is also important to note that there currently is no industry standard for measuring the amount of recharges a user can get from the battery. Some manufacturers test battery life using more strenuous tests that simulate job site applications, providing a "real measurement", while other tool manufacturers test cycle life using applications that are not representative of real-world job site applications. Users should be aware of this issue and be cautious of cycle life claims until a standard is established by the industry.
Rule 4: Higher voltage means more power and run time
When selecting a cordless tool system, the best place to start is with voltage as it is the best indicator of overall power and runtime. Higher voltage tools deliver more power and longer run time.
If a contractor's primary application is fastening small screws, a low-voltage system (7.2V to 14.4V) is ideal. For a contractor who needs to fasten screws and drill holes and use circular saws and reciprocating saws, 18V is ideal. Eighteen-volt tends to be manufacturer's broadest systems with the most tool options. If 18V isn't enough power and run time, consider a higher voltage (24V-plus) system.
After a voltage is selected, compare the features and benefits of the tool. This includes speed selections, ergonomics (size, weight and balance), tool-free blade or bit changes, clutches, battery type, hammer mechanisms, etc. Also, consider a combo kit containing multiple cordless tools.