Understand 18-volt battery technology and alternative power supplies.
Subject: Cordless Reciprocating Saws, Part 2
Topic: Power supply for cordless reciprocationg saws
Objective: Understand 18-volt battery technology and alternative power supplies
Task: Review 18-volt battery technology and explore capabilities of various power supplies for cordless reciprocating saws.
Part 2 of our series on cordless reciprocating saws focuses on the 18-volt battery, the saw’s primary power source. We’ll look inside a battery to understand how they work and address ways you can get the most out of your 18-volt rechargeable batteries.
The 18-Volt Rechargeable Battery
The standard power source for both the Milwaukee and DeWalt cordless reciprocating saws is the individual 18-volt battery. The battery consists of individual cells hooked together in series to provide the required 18 volts of power. The plastic battery case contains the connection terminals and a means to secure and release the battery from the handle of the saw.
All rechargeable 18-volt reciprocating saw batteries that DeWalt and Milwaukee sell are manufactured by Panasonic or Sanyo and are sold under the Milwaukee and DeWalt label.
The 18-volt rechargeable batteries are called "NiCads" because the material inside them that accepts and stores the electrical charge is nickel cadmium, a precious metal. Soon, manufacturers will introduce 18-volt rechargeable batteries made of nickel metal hydride, NiMH, a different and better performing metal. This new generation of reciprocating saw batteries will be capable of powering tools 55% to 100% longer than the current NiCads.
In 1998, DeWalt upgraded its 18-volt battery packs to assure better performance. All of DeWalt’s upgraded 18-volt batteries are marked with a yellow dot on the top of the pack. If you own an older battery pack, DeWalt will install this upgrade to your unit free of charge. Call 1-800-4-DeWalt for details.
How Do Reciprocating Saw Batteries Differ From Typical Rechargeable Batteries?
There are many myths and misconceptions about reciprocating saw batteries among fire and rescue personnel. Our greatest fire service experience with NiCads is as a power source for our portable radios or pagers.
As firefighters, our most fundamental belief about rechargeable NiCad batteries is that they develop a “memory”. Fire station discussions also include warnings of the “dangers” of recharging a partially used battery and war stories of how batteries left on chargers will get ?lazy? and not hold their charge when really needed. All these statements and others you may have heard about rechargeable NiCad batteries DO NOT apply to batteries used in cordless reciprocating saws.
Radio and pager NiCad batteries are not used in the same manner that we use 18-volt saw batteries. Similar to a marathon runner, portable radio or pager batteries discharge their energy slowly over a long period. The battery discharges a slow, steady current throughout the 12 or 14 hours that the unit is turned on.
Reciprocating saw batteries, however, are more like sprinters than marathoners. These batteries are used hard and fast during the brief moments of a rescue and undergo maximum draw for just a brief period. The current draw is so hard and so fast that the battery will actually heat up, sometimes significantly, as its energy is drained. Because of this inherently different way of drawing power, 18-volt reciprocating saw batteries WILL NOT develop a NiCad memory. In fact, the best place for a reciprocating saw battery is on a charger that is plugged into a power source.
A battery not in a charger unit loses 5% of its energy each day due to normal deterioration. When a battery is first placed on a DeWalt charger, the charging process begins with a rapid first stage charge. Initial charging of the DeWalt 1.7-amp/hour XR2 battery pack or the Milwaukee 2.4-amp/hour battery takes between 50 and 75 minutes. The DeWalt charger then transitions into a second charge mode that “tops off” the cells of the 18-volt battery. After 16 hours on the charger, a third stage that DeWalt calls its “maintenance stage” kicks in to trickle charge all cells to the fully ready mode. An 18-volt battery pack will eventually lose all its charge if left in a charger that is not plugged into an appropriate power source.