NiMH Battery Testing

Introduction

Since I’ve amassed quite a collection of rechargeable Nickel Metal Hydride AA batteries of varying brands, age and condition, I figured it would be a good idea to test and rate them all. This way, I’ll know which are my most reliable, which have the best capacity, and which are best relegated to lesser duties.

Process

First, I took each of my batteries and labeled them with a number for tracking purposes. Then, using my homemade battery tester and my Maha MH-C401FS battery charger I performed the following steps:

  1. Reset battery tester to 12 o’clock
  2. Charge battery on slow charge rate
  3. When fully charged, remove from charger and place directly into tester
  4. When the clock hands stop, record the stop time in the spreadsheet

My tester has two discharge rates: 480mA and 1200mA. I ran the test for each setting twice each battery, for a total of 4 trials per battery. Tests 1 and 2 were measured at 480mA and tests 3 and 4 were measured at 1200mA.

Analysis

Here’s my analysis spreadsheet on Google Docs. As you can see, there are a LOT of columns.

  • Columns A through E: describe the battery being tested
  • Column F: overall result – marked as bad if labeled as low capacity, inconsistent or failure prone
  • Column H: how long the battery lasted in the first test, in hours and minutes
  • Column I: the measured number of milliamp-hours for the first test
  • Column J: how the battery measured compared to its rated capacity
  • Columns L through V: results of tests 2 through 4
  • Column X: the average performance of the battery across all 4 tests, in mAh
  • Column Y: the standard deviation of all 4 tests (high numbers mean the results were less consistent)
  • Column AA: marked as yes if the battery averaged over 2000 mAh (high capacity)
  • Column AB: marked as yes if the battery averaged between 1200 and 2000 mAh (mid capacity)
  • Column AC: marked as yes if the battery averaged below 1200 mAh (low capacity)
  • Column AE: marked as yes if the battery performed inconsistently (high standard deviation)
  • Column AF: marked as yes if the battery performed very poorly (less than 500 mAh) on one or more tests. These batteries are judged to be unreliable, since they may not take a charge properly.

Conclusions

  • My Duracell 2650 mAh batteries cannot be trusted. Maybe I got a bad batch, but they were very unreliable. They’ll be taken out of service and recycled.
  • The Duracell 1800 and Energizer 2300 batteries are doing great, consistently performing near their rated capacity. This will be my go-to batteries for my digital camera, GPS, etc.
  • My old Kodak and Powerex batteries (both many years old) have lost some capacity but still perform consistently. They will be used in toys, radios, etc.
  • The old Qwest batteries don’t have much capacity left, but are consistent. They’ve been fine in low-drain devices like my cordless mouse.
  • The new Rayovac “Hybrid” batteries (standard NiMH batteries except with longer “shelf life”) are performing consistently and as advertised. I’ll be getting more of these for my camera so it’ll be ready at all times.

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