I bought a used 2007 Dodge Ram 1500 a few years ago, and for the first 15 months I had no trouble with parasitic draw or dead batteries or anything - I use one of those 150-Watt AC-to-DC power inverter strip in my center console, plugged into the auxiliary power outlet, so that I can charge various devices in the cab while I’m driving. I’ve used the same one for years in multiple different vehicles and never had any issue with parasitic draw, including in the first 15 months with the truck. I left it plugged it into the outlet at all times, even while the truck was off, and always the battery would hold its charge, starting just like normal even after multiple days without driving.
In January the truck battery died over a particularly cold weekend, and I assumed it was just at the end of its lifespan (it was already fairly old), so I replaced it with a brand-new battery. Two months later the battery died overnight again, but this time I was unsure why. I eventually noticed a correlation between leaving the power inverter plugged in overnight and discovering the battery had no charge when starting the truck in the morning, so I figured the issue was parasitic draw - but again, I’ve never had that issue before, despite using the same exact power inverter.
I figured maybe I had a bad alternator, so I had it tested for free at a few auto parts stores - both battery and alternator passed the tests every time. I’m aware those tests are fairly narrow, however, and can miss a lot of problems.
Is it possible there are sub-components of my alternator (e.g. the regulator) that are bad, which can cause apparent parasitic draw from devices that previously never caused parasitic draw? In other words, is there some single cause that can explain all of my observations over time, and is it likely to be related to the alternator?
After the battery died overnight again last week, I’ve had continuous trouble re-building or maintaining a charge, even though I never plug in the power inverter anymore. Does this point to a faulty alternator component? What might cause an alternator to pass a voltmeter test, but still fail to actually do its job? Is it possible there’s a connection between a bad alternator and the sudden trouble with my power inverter draining the battery overnight?
A bad rectifier/diode can cause a parasitic draw on the battery.
Key Signs to Look For
So, how to know if regulator rectifier is bad? In general, there are two primary ways that the regulator rectifier can fail. First, the diode can burnout and cause the battery to drain. You won’t have any trouble diagnosing the faulty regulator rectifier if the battery is the cause. You’ll note signs right away like poor starts, fluctuating meter readings, and dimmed headlights.
If this were my car, I wouldn’t leave the inverter plugged in. I’d guess that it draws some current even if nothing is plugged into it. That current might be minimal, but over the long term the extra discharging and charging might result in a reduced life for the battery.
My guess is your DC to AC inverter has developed a problem and is now draining the battery. Unplug it, leave it unplugged, charge your battery to a full charge with a battery charger, and see if that solves the problem. If so, replace the inverter.
You might ask how an inverter could fail and then drain the battery? Lots of possibilities, but the most likely: Inverters contain diodes, and diodes can fail with use. When a diode fails it may conduct current in both directions, when it should only conduct in one direction. Likewise alternators also contain diodes, and a common failure mode for an alternator, one of their diodes will fail and the symptom is a drained battery.
If you determine the problem isn’t the inverter, if you know how to use a volt meter safely, here’s the battery/alternator test I use: Before first start of the day the battery should measure about 12.6 volts; then immediately after starting the engine, 13.5 - 15.5 volts. Post your results here for more ideas.
Yes there is an internal component that will drain your battery even though the alternator “appears” to be working somewhat Okay. It might reach 13.8 but never reaches 14.4V. The battery will be drained while sitting after a few days to 2 weeks.
In the older Dodge that use the NipponDenso ND alternators (ND stamped into the back cover), there is a capacitor built in to the brush holder terminal block. It connects between the B+ Output stud and the chassis ground of the alternator. It is a film- or foil-type capacitor of about 0,5 to 2 uF designed to filter out high frequency noise in the 12V system voltage sent back to the battery for charging. The capacitor can degrade internally and cause a high impedance short circuit of the battery to chassis. The resistance of this leaky capacitor will be much higher than a direct short, which is what makes it so hard to troubleshoot.
For example i found a shorted capacitor in the terminal block that measured from about 1k to 10k Ohms. It would vary depending upon conditions such as temperature. When i measured the parasitic drain current is was about 40mA (0.040 Amps). This is very tiny but sufficient to drain a battery in 2 weeks of sitting, especially when the full output voltage of the alternator is never reached while it is running, and the plates never get that de-sulfating action that occurs at the 14.4V level. So the battery is getting weaker due to sulfation damage and it loses capacity, and it is constantly getting drained by the leaky capacitor in the alternator.
@kenny.house_191591
Welcome to the forum. Thank you for your detailed response to the OP’s question.
FYI, you happen to have responded to a discussion thread that is two and a half years old, so it is unlikely the OP will see your reply. If you look in the upper right hand corner of comments in a discussion, you will see when a comment was posted, such as 3 hours, or 2 days, or 6 months, or a date such as May 2022.
No harm in responding to an old discussion, especially when providing such detailed explanation as you have.
If you ever happen to have a question to pose similar to one you find in an old discussion, it is usually best to create a new topic discussion. That way your question is more easily seen and responded to.
Again, welcome to the forum. Do please stay and join in.
