I've been trying to diagnose a battery problem for many years now without success. I've read this forum, other forums, and many other tech sites trying to figure this out with no luck yet. I'll walk you through what I've checked so far, and where I currently stand. Perhaps some of you have some additional input.

Patient:
2008 PT Cruiser Base 2.4 non-turbo, non-convertible


Symptom:
Every 1-2 years the battery dies and needs to be replaced.
Battery tends to reveal that it's dying/dead on humid/moist/rainy days, usually winter time, but it just died this summer a few days ago for the first time.


What I've checked:
Alternator is charging (13.8V avg, with spikes up to 14.5V revving up and settling back down to 13.8V)

Battery Ref. voltage registered at the ECU is approx. 12.8V not running and 13.8-14.5V while running (read using ELM OBD2 dongle).

Starter tested every battery replacement and checks out without excessive load.

Firewall/Frame-rail grounds are good.

No Fog lights, so no bad switch like some experience.

No excessive current draw overnight (well under 1A and about 40-60mA avg.)

No bad door/hatch pin switches or misbehaving dome light (which the current draw test would reveal as well).

No misbehaving switches of any kind.

Nothing stuck in the cigarette lighter (current test would reveal this too).

No bad battery terminals or wires. They all appear in excellent condition for the age.

No aftermarket electronics of any kind.

No check engine lights or warning lights of any kind.





What I've done to "get by" in the meantime:
We never use the keyless entry anymore because it cuts the headlights on when you unlock. We've cut that battery draw out.

I went to a slightly oversized 85-2 DieHard Battery.

We start the car up anytime we use battery power (like to put up the windows, or lock doors) and let the alt. charge it back up for a few minutes.


No Diagnosis:
Despite ALL OF THIS, the problem continues. Literally EVERYTHING it could be keeps checking out as perfectly fine. Frustrating to say the least.


My current thoughts:
I've been as methodical and logical as I can in diagnosing it. I'm a former mechanic, who also has many years installing mobile electronics and doing custom wiring as a profession, so I'm very capable and knowledgeable unlike most diagnosis threads I've read. I can't find anything wrong with it, and I've certainly tried!

I'm beginning to think that the issue may not be an electrical issue, but a thermal issue.

I just had to replace the battery AGAIN a few days ago (last one went bad about 1.5 years ago), and this time I noticed something I didn't see before. 2 sides of the battery were semi-swollen and bulging. 2 sides were fine and not swelling. The 2 sides that were swollen were the long backside and short side next to the radiator (fully exposed to the engine bay temperatures). The 2 sides that were not bulging were facing away from the engine bay (towards the front behind the headlight, and on the side near the air intake port by the inner-fender). The 2 sides not swelling would naturally get cooler air just from their placement anytime the car is moving, while the 2 sides facing the engine bay get tons of heat from the engine as well as the hot air from the radiator, even when moving.

I have NOT confirmed this yet, but I'm throwing it out there since it seems to be the most likely possibility after eliminating EVERYTHING electrical I can think of.

In an attempt to try to confirm this, I purchased a thermal battery blanket (made for TJ Jeeps) that will isolate the battery from engine bay temps a little better. That thermal blanket happens to be roughly the same size as the slightly oversized DieHard 85-2 battery I'm using, and would also probably suit the stock battery just fine too.

Like I said, I don't know if this is finally going to fix the problem, but my mother absolutely loves her PT Cruiser, so I have to keep it around as long as possible.


Appreciated Input:
Is there anything else I'm overlooking electrically that I could check?

Anyone else have any kind of similar phantom "electrical drains that aren't drains" with their PT Cruiser, and if so, did you find the problem/solution?

 

So how often is it driven ? you said its your mothers that would lead me to believe not so often. What area do you live in as well.

 

Driven every day with about 4 start/stops and approx. 40 miles each day.

We're in central FL. Heat is certainly a factor, and lately the ambient temp on the dash has been registering over 105deg F.

 

SO likely the water is being boiled out of the chambers then. Check the water level under the caps.

 

The battery was just replaced less than a week ago. I always have the batteries tested before replacing, but have yet to look at the water/acid level. When maintenance-free batteries took over as the default many years ago, I kinda stopped even checking or topping-off like we used to do a decade or more ago. We've been using these gold 85-2 batteries for the last 3 replacements and they are maint.-free:
https://shop.advanceautoparts.com/p/...5-2/99996789-P

If that long vent tube cover pops off easy enough, then I think I'll be adding battery level checks to the every 6mo maint. checks list I have going.

Perhaps the thermal battery blanket may end up helping like I'm expecting at this point.

Thanks for the input!

 

I can share what I've found with my pt cruiser.
I was stumped everything tested ok until I checked alternator regulator several times over a couple days. The regulator is tucked away inside the pcm and isn't serviable.it selldom fails but it does fail intermittent and inconsistent.overcharging then not charging then under charge at random. Over time it killed 2 batteries and corroded battery and alt wires.it took awhile to find it being intermittent but it will show itself.maybe not your cars prob. But it happens apparently often with pt pcm good luck

 

The PCM went bad (internal short) about 5 years ago, and was replaced and programmed at the local Chrysler dealership. The dying batteries is a separate issue that existed prior to that problem, and after, so no direct correlation I can find. I have zero corrosion issues. To be honest most of you would be absolutely jealous of the excellent condition of the terminal connectors and cables. Zero corrosion, ever, and still look new. For that reason I'm going to lean in the "probably not" side.

Thanks for the input! Exactly kind of odd-ball things I'm looking for since everything consistently checks out.

 

I failed to mention there's a bunch of fusible links in the batt and charging systems. A lead into PDC appears to split into 3 or 4 fusible links. I doubt that's related but they can be sneaky hiding inside closed harnesses. I.e. tcm ignition pcm. I found em under battery tray. That's my random thought today. Yesterday I suggested Chrysler engineers get drug tested they really are good at over engineering.

 

Posted another new topic (window regulator) and thought I'd check back with this one.

Like I said before, I just replaced the battery AGAIN, and am now using the thermal blanket to try to keep heat soak from being an issue. I will also be checking the water level every 6 months and topping off with distilled water as needed. We'll see how well it holds up this time. No issues so far (only been 3 months).

One tip I wanted to share is:
Battery warranties are good, but having a good relationship with your local parts store is even better.
The warranty only covered 1 replacement within the warranty time frame.
My relationship with my local parts store got me 3 replacements free of charge within that warranty time frame.

Time will tell if we finally broke the battery-killing cycle, but this could have been a much more expensive situation if I didn't have that good relationship with my local parts store and the people who work there.
Thought it was worth mentioning.

 

If you ask me, I noticed on my PT Cruiser (2001) that the cables to and from Battery (thick terminal plus minus cables) and clamps at the battery are cheap and frail. Maybe good ones need to be installed.