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x86 Instruction Chart
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9 Volt Battery Chargers
Solid State Circuit Breaker (20V 650mA)
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Ohm's Law Calculator
Prime Factorization
Convert a Decimal Fraction to a Simple Fraction
Example POV-Ray Animation
Example Virtual Machine
Locating a Gunshot with an Array of Microphones
Software Defined Radio
Salt Flats & Aeromods
Audio Amp + Spice References
Image Processing
KFC 'Secret' Recipe
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Railroad Tracks
The Bike Shed
The Guy That Invented Fire
Mods for the TRS-80 Color Computer

9 Volt Battery Chargers

Charge Rate

Charge Rate for a 9 Volt Battery
Everything I need to know is on the label!

You need to know three things to charge a battery.

  1. Voltage
  2. Amperage
  3. Time


The voltage the charger outputs in not really that important as long as it is more than the battery voltage. How much more? Enough to overcome the internal resistance of the battery, and push the stated amount of current through the battery.


  • Whatever it says on the label.
  • If not, a normal charging rate is the Capacity of the battery C divided by 10 or C/10.


  • Whatever it says on the label.
  • Long enough to put 44% more power into the battery than it's Charge Capacity
  • 14 hours at C/10
  • Or you can detect when the battery is charged

From Garden State Battery

The most common and reliable method for charging cadmium-based batteries (NiCd and NiMH) is the "Negative Delta V" method. This method senses a fully charged battery by detecting a drop in cell voltage as the battery reaches capacity. This drop is small but noticeable enough to be detected and signal the charger to shut off or to trickle depending on the charger type. Other chargers use "Delta T" or change in temperature sensors to decide when to stop charging. "Delta T" chargers are less reliable and many manufacturers have adopted the "Delta V" or a combination of the two as their preferred method of choice.

Method I'm Choosing

I'm not going to try to detect when the battery is charged. I'm just going to charge my 9V batteries at 11ma for 14 hours just like it says on the label. They might get slightly overcharged, but they will get fully charged. Then I will be able to rule out charger malfunction as a cause of my problems.

Back Next

Charge Rate

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