Marine and Car Battery Drain Test: Find Reasons to Stop It

Just filling up the gas tank is never enough to run your car effortlessly. It takes much more than that. The battery you have underneath the hood of your car provides the energy to start your engine and alternator supply. So, you need regular car battery drain test for testing the present condition of your car and then take action.

Well, a marine and a car use same AGM batteries for their vehicle, so where we discuss a marine battery it’s actually same as discussing a car battery. So, we will discuss both of the action while talking about the drain test.

Car Battery Drain Test: Stop the Battery Draining

The maximum car owner has experienced a certain incident and that is a walk to the office or the destination walking or talking taxi cab instead of driving by his/her car because the car was not starting. Your car won’t start if the battery of your car doesn’t work accordingly.

The battery provides necessary current supply to electrical units and also stabilizes the fluctuation of voltage while driving. So, the maintenance of the battery should be one of the top priorities for an owner or caretaker of a car.

Step 1 Testing the battery

One of the major issues for the trolling motor and cars is the unknown state of the battery. So, we need to run parasitic drain test to find out the current state of that trolling motor battery or the battery in the car. You will need a digital multimeter (20-amp fuse and 200 mA reading capacity) as the parasitic battery drain tool, eye protection goggles, and gloves.

parasitic drain test

1.      Need fully charged the battery:

Before running the parasitic battery drain test, you need to stop the vehicle. Turn off all the accessories in your automobile including the GPS, phone charger etc. Because ever the phone is not connected to the charger but the charger is plugged in, draws current from the battery. We need a fully charged battery, so unplug and disconnect them all.

Remove the main fuse for the modified stereo system if you have one, which uses supplementary amplifiers for subwoofers or speaker or both of them as they draw a huge amount of energy from the battery even when the automobile is off. Turn off all the lights, shut the doors and turn off the ignition and then remove the key. By doing these you’ll get a fully charged battery. After this test, you can easily install the battery to boat or car.

2.      Connect the amp meter to the battery

Connect the amp meter in the right sequence to your battery or the electricity supply system. Disconnect the negative battery wire from the negative terminal of the battery. The negative wire is the black one connected with the battery postmarked (-) on it. Connect the negative probe (black) of the amp meter to the negative post of the battery and connect the positive probe (red) of the amp meter with the disconnected negative battery terminal.

Set the DC scale of the amp meter to the highest and switch it on. The meter should show zero amps on its display. Now start moving the dial to a lower setting until you detect any sort of existence of current.

Connect the amp meter to the battery

If your automobile has parasitic drain trouble the current will be over than 50 mA (milliamps) and if not, then the current will be within about 50 mA range.

Also, if the reading doesn’t cross the range, then your battery is a case of defective charging system or defective battery.

If crosses the range or the reading is within 1 mA to 10 mA, then one or more electrical circuits are faulty.  Leave the amp meter connected and use two plastic clasps to hold the negative and positive probes with the terminal of the battery, and then make sure that the automobile is turned off during the process. Now, you can go to the next step.

Step 2 Find out the reason and Stop it

While making the full marine and car battery drain test, you need to find why the battery is draining and then take actions to stop it. It will make the battery last longer with providing better charge for your trolling motor or cars. These tests will make using the deep cycle batteries safer and useful.

1.      Spotting the faulty circuits:

While parasitic drain on battery probable causes, one needs to consider spotting the faulty circuits. But without proper knowledge and experience, you may not go far with this cause. So, I am going to suggest some steps to make the whole process a bit easier.

  • Start taking off the fuses from the fuse boxes of your automobile, one at a time. If there is an underhood fuse box, start with it. Disconnect one of the fuses and follow the reading of the meter, if meter reading doesn’t come back to a normal range that is within 50 mA then it’s not the faulty one and reinstalls Now continue the same process until the meter reading come back to the normal range. When it does means the circuit protecting the fuse you just pulled out is the faulty one.
  • After finding out the faulty circuit that is causing the drain, open the lid of the fuse box and check the circuit description. Something, You will find the writing such as “blower motor 30-amp fuse”, “Tail, parking, side marker lamps” or “Radiator cooling fan”.
  • Use the manual for repairing of your automobile to find out the diagram of wiring for that circuit. The diagram is about the switches, connectors, and loads placed in that specific circuit, which is the possible troublemaker.
  • If there are any switches, begin with it to be sure that they are perfectly operating.
  • Keep away the cables in the circuits from the heated surface and the connections of the loads and connectors are clean and sturdy.
  • A loose or burned wire at a load or connector can cause a short So check it too. 

Car Battery

Source: Mechanicable

2.      Look for other reasons

When I first thought of addressing this issue in my blog, I first read a lot of blogs and forums to know what people actually want.  A lot has been found in the subject: parasitic battery drain found how to fix. But I had to cut some of the questions out of them to focus on the most important ones.

And apart from circuit problems, there are some other issues we need to address. If the circuit is not the problem, then there are some other different reasons your car battery is draining to explore.

  • The lights can cause the battery drain. Check out the glove compartment and trunk thoroughly if the lights in them are on. Check if after closing the glove compartment or the trunk the lights are on. If it is found out why and solve them. These could be the culprit because lights drain a huge amount of current from the battery.
  • It could be the car alarm. If the car alarm is faulty or the connections are faulty, it can drain a full charge battery in a couple of days.
  • The stereo system can be a reason for the drain. Stereo system with additional amps for the speakers can drain a huge amount of current from the battery if the wiring is faulty.


If you are using this battery on a kayak for fishing, then checking the battery drain regularly is a must. The troublemaker is never an absolute one. So, check and cross-check the procedures we’ve discussed. Maybe the spotting faulty circuit procedure is a lengthy one to perform but is one of the most effective on. So, hope you find the culprit causing the problem to your battery and repair it.

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