How to Burn Test Your Underwater Light

So you have decided to add a primary HID/LED light to your equipment bag. There is a significant investment to purchase primary lights. They don’t come cheap. A good quality primary light can cost up to $2,000 USD, even more for high powered video lights. You need to make sure your investment will last as long as possible. One of the preventative maintenance procedures for checking the health of your primary light is to burn test the battery. Burn testing the battery is a simple procedure, but does require some time. This will give you an accurate measurement for how long your battery will hold a charge.

Before we go into the procedures about how to perform this test, let’s take a look at why you should be doing this test. The burn test will give you a pretty accurate reading for how long your light will last on a full charge. For divers who are diving in overhead or dark environments, this is critical as nothing will ruin a cave/wreck dive more than a light failure. For recreational divers, who do not venture into overhead environments, the burn test will tell you the health of your battery. If the consecutive burn test results show that the battery is holding less and less of a charge over time, then you may be purchasing a new battery soon. Batteries aren’t cheap either.

How often should you burn test your battery? That depends. If you are a recreational diver, staying out of overhead environments, performing the burn test once or twice a year is prudent. For cave and wreck divers, a highly reliable primary light is very important. These divers should burn test their batteries more frequently. I have found myself burn testing mine two to three times a year. Now that I will be doing more cave diving in the winter, I’ll probably end up burn testing mine four or five times a year.

There are some simple tools you will need in order to perform a burn test:

  • Your light head and battery
  • Volt meter or multimeter
  • Timing device
  • Bucket of water (for your light head)
  • Uninterrupted free time

Burn Test Procedures

Before performing the burn test, you need to make sure your battery is on a full charge. I will charge mine till full, then let it sit on a maintenance charge for about an hour after the full charge. Then I hook up my light head to the battery and leave the light turned on for about ten minutes, with the light head in a bucket of water. Then I put a final charge on the battery. Once full, you will be ready to start the test.

  1. Place the light head into a bucket of water. HID lights specifically need a way to remove the heat buildup from the bulb so that no damage occurs to the bulb. A bucket or sink of luke warm water is sufficient enough to keep the bulb cool. Just make sure water stays in the sink or bucket.
  2. Connect the battery to the light head. Leave the battery out of the canister. This will make it easier to connect the volt meter to take readings.
  3. Connect your volt meter to the battery. Most volt meters have simple metal probes. Make sure that you stick the probes far enough into the Anderson connector to get an accurate reading. If your light head connects to the battery with some other form of connector, then make sure you can attach the probes to the wire. Once the probes are connected, take your reading from the volt meter and record the reading. If this reading is at 10 volts or below, your battery is most likely bad.
  4. Turn on your light head. Take another reading with the battery under a load. This will be your starting voltage. Set your timing device to alarm after 10 minutes.
  5. At every 10 minute interval, take another reading with your volt meter and record the reading. Stop taking readings when the battery’s volt reading is at or below 10 volts. Do not leave the battery unattended. Once the battery drops below 10 volts, it will start to drop more rapidly. You do not want the battery to drop below 10 volts.
  6. The total amount of time it took to get down to 10 volts will be how long your battery will last. I record this time and the date of the burn test on a piece of duct tape on the battery. This way I know how long the battery will last so I don’t get it confused with other batteries I may have laying around.
  7. Recharge the battery immediately

You don’t want your battery to drop below 10 volts or completely discharge. Doing so can damage the cells inside the battery pack. For this reason, if you do not use your light for a long period of time (like over the winter), you should place the battery on a charge occasionally.

It should also be noted that the minimum discharge voltage may differ for battery packs from different manufacturers. For example, some manufacturers for lithium ion battery packs recommend the batteries to not go below 8 volts. However, never taking a battery below 10 volts is a good guideline. See the manufacturers recommendations prior to conducting the burn test on your battery.

The burn time for your battery will vary depending on the light head used in the test. My primary light is an 18 watt light head. This light head will consume more battery power than a light head with a 10w rating. While a 10w light head may give a burn time of six hours or more, my 18w light head gives me a burn time around four hours. A light head with a higher output, will consume more battery life and give a shorter burn time.

There are devices that you can hook up to your computer that will analyze the battery. These analyzer can control the burn test process such that the battery doesn’t become complete drained and preventing damage to it. Certainly a nice tool to own. I’ve seen some of these selling for about $200. If I had more lights, this would certainly be worth the investment.

Primary light photo copyright Halcyon –

About Duane Johnson

Duane Johnson is the founder of Precision Diving and runs a scuba diving blog to help scuba divers improve their diving skills and enjoyment. He teaches recreational and technical scuba diving classes in the Chicago area. Learn more about him here and follow him on Twitter at @PrecisionDiving.