Battery Life

I had an experience a few weeks ago whereby I couldn’t join the ORCA net on my vx8-dr because of a low battery. From that, I thought I’d run a test to look at how long different types of batteries run in the vx8-dr. The basic protocol is to setup the vx8-dr to transmit APRS location messages on a regular basis and measure the battery voltage over time. The voltage measurement comes from the vx8-dr itself. Yes I’m trusting that it was accurate but with the test running the same way across all the types of batteries, I think it’ll be a valid test. Besides, the reading from the vx8-dr is what I’ll be using in the field.

The vx8-dr can use 4 different types of batteries: 2,000 mAh lithium ion, 1,100 mAh lithium ion, AA alkaline and AA lithium ion. I ran a set of tests over the course of 8 days.

2,000 mAh lithium ion

vx8-dr 2000mAh

relative time voltage
0:00:00 8.2
1:04:28 8.1
2:05:27 8.0
3:14:07 7.8
4:58:20 7.7
6:04:41 7.6
6:46:38 7.6
7:43:17 7.5
8:34:24 7.5
9:30:31 7.4
11:21:29 7.3
12:22:51 7.3

1,100 mAh lithium ion

vx8-dr 1100mAh

relative time voltage
0:00:00 8.2
0:00:00 8.2
2:15:51 7.8
3:06:14 7.7
3:58:57 7.5
6:27:44 7.4
8:01:43 7.1

AA alkaline

vx8-dr aa alkaline

relative time voltage
0:00:00 4.2
0:43:23 3.9
1:26:23 3.8
2:02:19 3.7
2:46:57 3.6
3:43:42 3.6
5:02:25 3.5
8:15:51 3.3

AA lithium ion

vx8-dr aa lithium ion

relative time voltage
0:00:00 4.5
1:23:24 4.3
3:33:47 4.1
5:19:44 4.1
9:04:00 3.9
9:55:36 3.9
20:56:06 3.7

I unintentionally left the vx8-dr running over night and the battery level only dropped 0.2 volts. That was very unexpected.


I came to a few conclusions from this test:

  1. Measuring the voltage will most likely be a good way to keep track of when to change batteries.
  2. Just measuring the voltage doesn’t provide any data on how well the transmitter is working with the available voltage / power.
  3. Judging by the AA lithium ion battery test, I need to re-run the 2,000 mhA and 1,100 mHa test. It looks like the voltage level of the lithium ion batteries may not be linear. That may put a kink in the use of the battery voltage to determine remaining power.

I’ll re-run the 2,000 mHa and 1,100 mHa tests over the next few days to see how long the batteries last. Perhaps lithium ion batteries don’t have a linear voltage level over regular usage.

More importantly, I need to expand the tests to determine the output power level as the batteries are used. I’m not yet sure how to do that. Maybe it’s time to invest in an RF power meter.


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