Fixing modern car battery run downs

I sawyour column and was hoping that you could offer suggestions formy battery issues. I have a 2017 Honda CRV Touring with about 8500 miles on it. When the vehicle sits for 3-4weeks, the battery drains to the point I can’t start the vehicle. The last time after 3 weeks, it was so depleted that I had to use the emergency key to open the doors to get at the hood latch. My wife’s 2017 Honda Civic sits the same length of time and starts right up. The weather has been in 60F-80F range and the vehicles are garaged. The vehicle has been back to the dealer several times underwarranty service to look for problems. The last time they said that they found a bad cell in the battery and replaced it. The dealer told me that it is normal for vehicles that sit for 2-4 weeks need to have a “jump”. I have had cars and trucks for close to 50 years and never encountered a vehicle that it is considered normal for the battery to be dead after 2-3 weeks. I have searched online and found other people complaining about similar issues. My fear is that there is a bigger problem with the vehicle and when the warranty runs out I will be responsible for finding and fixing what ever is causing this. Any suggestions? — Bruce B.

This will give me another chance to go a little deeper into the realm of parasitic drain! Your Honda is far more sophisticated than Drake’s van. Your body control module, for example, stays awake for about ½ hr after the key is turned off just in case you’re in the middle of a blue tooth connected phone call. It’s possible the BCM isn’t properly going to sleep due to a faulty door switch input or other situation. Other modules need to go to sleep as well eventually when parked. What’s needed is a parasitic drain test. This involves using an inductive ammeter clamped to one of the battery terminals, observing battery drain as the modules nod off. This method is less accurate than the next to be mentioned, but is quick and easy to do.

Separating a battery terminal with an ammeter lead clipped to terminal and the other lead held to post is a more accurate method of checking for drain, which should be perhaps 50mA or less depending on vehicle model. Assuming an objectionable drain was seen, the next step is to narrow the search to the offending circuit. One method is removing fuses one at a time while observing the drain, this requires perhaps three hands! Another (battery is reconnected) is to measure voltage across the two tiny slits of each and every fuse (fuse is in place). Red meter terminal to one slit, black to the other. An inactive circuit will read true zero volts. One with activity will show a tiny voltage drop as the fuse acts as a resistor of sorts. The trick is to know what’s normal/ what’s not, and some fuses protect multiple circuits, requiring further dividing and conquering.

It’s true a modern vehicle will run down the battery if parked for long periods (perhaps 4-5 weeks or longer). I think the 3 week rundown is excessive, something is going on that might be corrected. A 100-200W dash-top solar panel connected to the data link connector can help until it’s fixed, assuming there’s sun. (accessory/lighter socket isn’t active on many vehicles when turned off ). In a garage, an underhood mounted smart charger, 120v cord end protruding from the grille, might be an answer.