My Cordless Drill - Death of nickel-cadmium (NiCd), arrival of lithium-ion (Li-Ion)

by Ivan Hamilton 7/10/2008 11:48:00 AM

A few years ago low-cost rechargeable drills/drivers hit the market. I purchased a nice GMC 18V driver with two batteries.

It's given good service over the years, but:

  • the batteries don't hold as much charge as they used to
  • the batteries don't hold their charge as long as they used to
  • recently, the "charger" (timer & battery clip) died
  • recently, the plug-pack transformer died

The drill itself is perfectly fine, and I've worked around the charger & plug-pack issues, but the time had come... the batteries died completely.

Professional cordless tools often have replacement parts available, but my drill was only a consumer level item and years later, is completely superseded. A number of people have had success rejuvenating cordless tools by "repacking" the batteries. Often, the battery packs for these tools consist of a number of series wired "Sub-C" cells (18V = 15 x 1.2V Nickel-cadmium cells). At $3-$5 per Sub-C, that's $90-$150 for both packs. After making such an investment, a much smarter (and safer) charger would be justified. If the charger is not "smart" (i.e. it cannot detect when the battery is fully charged), then overcharging is likely, which will damage the battery.

With a new 18V drill + two batteries available for AU$99, repacking didn't make economic sense. Armed with the experience from my first, my wish-list was:

  • 18V - I like the power from the 18V driver, and want to keep that. 
  • Geared - My ungeared driver wasn't fast enough for drilling wood or plastic, but I still need power for driving screws.
  • Low self discharge - Sometimes I won't use it for weeks, I want it ready to go.
  • Smart charger - If I need to charge a half used battery for use tomorrow, I want to not think about it (and not  damage the batteries).
  • No hammer action - Even with the hammer action disabled, hammer drills have an amount of axial play that interferes with accurate bit placement.

Any geek worth his salt knows a little about batteries (phones, laptops, etc): Nickel-cadmium (NiCd) then nickel metal hydride (NiMH) then lithium-ion (Li-Ion) then lithium ion polymer (Li-Poly) cells. The latest professional cordless power tools have started to use lithium-ion (Li-Ion), and in my scouting around I found the Bosch PSR 18 LI-2.

What do I like?

  • At AU$250, it's much cheaper than other Li-Ion drills on the market at the moment.
  • The lithium-ion battery is only about half the size & weight of comparable NiCd batteries.
  • 18V power
  • 2 speed gearbox
  • 85 percent of the charge is retained, even if it has not been used for four months.
  • Charging station is automatically switched off when the battery is fully charged (with no memory effect, these batteries can be recharged at any time without reducing their charge capacity.
  • Interrupting the charging procedure does not damage the battery.
  • Not a hammer drill (no axial play)

With all the smarts included to prolong the life of the battery, I figure it should give twice the value of a $99 Nickel-cadmium (NiCd). Time will tell...

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Mechanics | Pragmatism

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7/18/2009 6:33:41 PM

I was just thinking about My Cordless Drill and you've really helped out. Thanks!

Tools UK

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Name of author Ivan Hamilton
"My inner nerd can beat up your inner nerd."

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