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There are currently three choices when it comes to battery packs for cordless power tools. The first and most widely used is the Nickel-Cadmium (NiCd) battery. The second not as widely available is the Nickel-Metal-Hydride (NiMH) battery and the newest rechargeable batteries on the market, the Lithium-Ion (Li-Ion) battery.
NiCd and NiMH battery packs supply voltages from 2.4 to 18 volts and have been used for some time to power cordless tools like drill/drivers, reciprocating saws and small circular saws. Li-Ion batteries are a new development in cordless tool batteries that can supply higher voltages, currently up to 36 volts for DeWalt tools. Higher voltage translates to higher torque making it possible to build cordless power tools that rival or surpass the performance of most corded power tools.
Rechargeable Battery Packs Battery packs for cordless tools are built using several individual cells wired together in a series, similar to an electronic device where 2 or more AA or AAA batteries are joined together to supply the needed voltage.
Adding the voltage of each cell, many voltage levels can be achieved. Individual NiCd and NiMH cells supply 1.2 volts each. Ten of these cells wired together make a 12 volt battery pack (10x1.2=12). Eight cells make a 9.6 volt pack, 12 make 14.4 volts, etc.
NiCd and NiMH power tool battery packs are limited to about 18 volts due to the cumulative weight of the cells. The 15 cells required for an 18 volt NiCd/NiMH battery pack is about the limit for manageable tool weight. Li-ion batteries are changing all that. Because lithium is much lighter than NiCd and NiMH the cells are much lighter, allowing for more cells in a battery pack. This translates to higher voltages and more torque for cordless power tools. Li-ion cells supply 3.6 volts each. Ten of these cells wired together provide 36 volts which is the maximum Li-ion battery pack currently available.
At first glance it would seem that Li-ion batteries will make NiCd and NiMH batteries obsolete but that's not the case. First, the cost of a Li-ion powered tool is about twice that of the NiCd and NiMH counterparts, an unnecessary expense for most people.
Second, the extra torque possible with higher voltages is rarely needed by the average user. NiCd and NiMH battery packs can deliver more than adequate power for most purposes. Li-ion powered tools are intended for heavy construction work where, up until now, builders have been tethered by corded tools when real power is needed.
Memory Effect NiCd and to a lesser extent NiMH batteries can suffer from memory effect due to repeated discharge/recharge cycles at the same level each time. This creates a sudden voltage drop each time the battery reaches that level. This is a common problem with cell phones and other electronic devices that are operated for the same period of time repeatedly. Because power tools are operated at various levels thru out the discharge period, memory effect is not usually a problem. Some chargers have an equalizing mode that reconditions batteries that have developed memory effect.
Another effect found with NiCd batteries known as "lazy battery effect", occurs with repeated overcharging. This effect is evident when the battery is removed from the charger fully charged but discharges quickly after brief use. This effect can be reversed with repeated deep discharge cycles. The charger maintenance cycle will recondition batteries with this problem.
Chargers and Charging All rechargeable battery packs for cordless tools have special charging needs. The charger that comes with the tool should have functions to control temperature, charging speed and maintenance of the charge level. One hour chargers are the standard for most makers, however 15 minute chargers and 12 volt automobile chargers are also commonly available. Ambient temperatures should remain between 40° and 105°F while charging NiCd and NiMH batteries, otherwise battery life can be reduced.
DeWalt chargers included with all their NiCd cordless tools will charge all voltages of NiCd and XRP battery packs they offer. Their Li-ion charger will charge all their Li-ion powered tools. Makita offers a chargers that will charge all voltage levels of both their NiCd and NiMH packs. Their 18 Volt LXT Li-ion charger works with all their LXT tools. Milwaukee has a line of chargers with various capabilities including a combination Li-ion and NiCd charger for their 18 and 28 volt tools.
Below is a comparison chart for the three types of cordless tool battery packs.
| Battery Packs | Advantages & Disadvantages | Chargers |
|---|---|---|
|
Nickel Cadmium (NiCd) 2.4-18 volts |
+ Least Expensive + Least Temperature sensitive + Many Recharge Cycles (~2000) - Discharges 20% 24hrs. out of Charger - Cadmium is Environment Hazard |
DeWalt NiCd chargers are compatible with all their NiCd cordless tools. All their chargers have conditioning cycles for optimum battery life. Makita Universal chargers will charge all voltages and both NiCd and NiMH battery packs. Milwaukee offers chargers with various features. |
| Nickel Metal Hydride (NiMH) 2.4-18 volts |
+ Less Memory Effect than NiCd + Not as Toxic as NiCd - Fewer Recharge Cycles than NiCd (~1000) - Self-Discharge is Much Faster than NiCd |
Makita Universal chargers will charge all voltages and both NiCd and NiMH battery packs. |
| Lithium Ion (Li-ion) 3.6-36 volts |
+ No Memory Effect + Very Low Self-Discharge + Many Recharge Cycles (~2000) - Expensive |
Lithium-ion batteries require controlled conditions for charging to limit heat and chemical reaction. Only the charger included with the tool should be used. |
