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I'm about to buy a cordless tool set in which the tools all operate off the same form-factor battery. The batteries come in several different chemistries and I'm wondering which type is better for the type of short duration, impulsive discharging that power tools undergo. The available battery chemistries are:

  • Lithium Ion
  • NiMH
  • NiCd
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2 Answers 2

up vote 12 down vote accepted

There's a GREAT article here. I'd highly recommend checking it out. Here's a brief excerpt (ALL CREDIT GOES TO THE ORIGINAL AUTHOR!):

Nickle Cadmium (NiCd)

Pros:

  • NiCd batteries are more difficult to damage from heat and impact.
  • NiCd batteries have a longer cycle life of about 1,000 charges.
  • They put out strong current flow.
  • They are less easily damaged by being stored in deep discharge, although it is still not recommended.
  • They are less expensive than other rechargeable batteries.

Cons:

  • Nickel Cadmium batteries are the heaviest of the three types.
  • Lower capacity than other batteries.
  • NiCds shouldn't be allowed to drop below about 70% charge between charges, or the battery lifetime can be shortened.
  • Most NiCd batteries must be allowed to cool before being recharged.
  • Must be allowed to deep discharge about once a month or they will suffer severely from memory effect.
  • The cadmium in NiCd batteries is very damaging to the environment and must be disposed of correctly.

Nickle Cadmium Overview:

  • cycle life: long; 1000+ charge cycles
  • self-discharge: moderate, 15%-20%
  • capacity: low; 1.2 Ah - 2.2 Ah
  • optimal charge time: fast
  • maintenance: high; deep discharge once/month
  • memory effect: high if not maintained properly
  • sensitivity: very tough

Nickle Metal Hydride (NiMH)

Pros:

  • NiMH batteries are a little lighter than NiCd batteries.
  • They have a higher energy density, meaning that their capacity is greater than NiCd batteries, running 2 to 3 times longer in a single charge.
  • They are less expensive than Li-Ion batteries.
  • Capacity loss can be reduced drastically if charged and stored properly, making it possible to greatly increase their cycle life.
  • They are not destructive to the environment.

Cons:

  • NiMH batteries are more sensitive to temperature, especially cold temperatures, and should only be stored or operated between about 33°F - 103°F.
  • Deep discharge and lack of use will damage NiMH batteries, shortening their lifespan and limiting their storage capacity.
  • Should usually be charged after reaching 70% capacity, but should also be allowed to deep discharge every three months to avoid memory effect.
  • They are more expensive than NiCD batteries.

NiMH Battery Overview:

  • cycle life: varies; can be as long as NiCd if stored and charged correctly.
  • self-discharge: fast; 20%-30%
  • capacity: moderate; 2.2 Ah - 3.0 Ah
  • optimal charge time: fast
  • maintenance: moderate; deep discharge once/three moths
  • memory effect: moderate; can be avoided with proper charging
  • sensitivity: very sensitive to temperature

Lithium Ion (Li-Ion)

Pros:

  • Li-Ion batteries are the most light-weight of the three kinds of rechargeable batteries.
  • Li-Ion batteries benefit from high energy density like NiMH batteries do.
  • They are much less sensitive to damage from temperature changes than NiMH batteries.
  • Li-Ions are not restricted in the shape of their design like NiCd and NiMH batteries are, and can be designed in almost any shape for better tool balance.
  • They do not suffer from self-discharge and memory effect like NiCd and NiMH batteries, meaning that they're much less sensitive to recharging and storage methods.
  • They have the longest charge/recharge life cycle of all three types of batteries.
  • Li-Ion batteries are not destructive to the environment.

Cons:

  • Excessive overheating of Li-Ion batteries can damage or destroy them, which can occasionally happen during recharge. However, most rechargers and Li-Ion batteries are designed with safety features to prevent overheating.
  • They have the shortest overall life cycle of about 300-500 charges.
  • Li-Ion batteries are the most expensive batteries of these three types.

Li-Ion Battery Overview:

  • cycle life: short; 300-500 cycles, or about 2-3 years.
  • self-discharge: very slow or not at all.
  • capacity: high; 3.0 Ah+
  • optimal charge time: moderate
  • maintenance: none
  • memory effect: none
  • sensitivity: sensitive to heat and impact
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1  
this is comprehensive! –  Joel B Nov 25 '10 at 6:47
    
I agree. Again, credit goes to the original author. =) –  Mike B Nov 25 '10 at 19:41
    
great reviews. I have stayed with the Nicd batteries because of the life span, and durability. The prices are always a concern, but since I have about a dozen battery operated tools (Dewalt & Ridgid), i find the cost to replace nicad is dropping a bit, especially Dewalt. –  shirlock homes Nov 28 '10 at 14:46

I don't have any experience with NiMH batteries, but I can say for sure that Li-ion beats NiCd hands down. Especially for homeowner use, where the battery may sit for days or weeks off the charger, their lack of self-discharge is a key feature. There's nothing more frustrating than needing your cordless tool only to find the battery's dead. The lighter weight is nice too, as is not having to worry about any memory effect.

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I'm kinda scared because I've read that Li-ion batteries are more sensitive to temp and can actually explode if left somewhere really hot (like the trunk of a car perhaps...which I could foresee me doing). –  Joel B Nov 25 '10 at 18:06
    
Duly noted -- I had not heard that. I've never left mine in the car, but I have used them outside in sunny, hot weather and have not noticed any performance issues (including explosions!). –  Mike Powell Nov 27 '10 at 19:40
1  
Note that Li-Ion is what is in most laptops, and while there's occasionally stories about particular batches having explosion problems, there are a whole lot of laptops out there without problems. Though they're probably not treated quite as roughly as power tools (says the guy that just got his laptop back from repair for damaged caused by dropping it :-). –  Sean Reifschneider Dec 6 '10 at 7:42

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