Battery randomly draining for no explainable reason

[crushrus]

2003 van...

A few weeks ago I swapped the reverse lights for led bulbs.
A day or two later I went to drive it and it was completely dead. I thought maybe I just didn’t shut a door all the way or left a light on, so I jumped it, no big deal. Ever since then it will randomly just drain itself. I got a new battery, tested the old one, it was bad. Figured that was the problem. New battery worked fine for a couple weeks but now it’s done it twice in the last week.

I have no idea if the reverse bulb situation is involved, it’s just the first time It happened. It’s also strange because it doesn’t always happen. I’ve gone a week without driving it, start right up, then the next day it’ll be completely dead. No click, no nothing. Electrical stuff is already a nightmare to chase down, intermittent is even worse. The obvious thins (interior lights, etc) are not the culprit. No phone chargers in the cigarette outlets. All the interior lights, stereo amp etc are running off a second battery in rear that runs off a splitter, so it never drains the main. When the front bat is dead, the rear always shows full charge.

I’m at a total loss on this, Anyone ever experience anything like this? Anyone have any advice or ideas? Thanks!

[Astrophysics]

Hi,

Do you have the 125 amp diode isolator to separate the starter battery from the house battery, and is this what you mean by splitter?

Check for loose wire at battery isolator.

Also, note that a battery isolator has a diode drop og about 0.6 volts due to the junction drop in the silicon diode.

This can cause a situation whereby the alternator cannot fully charge the battery. Some users now use automatic charging relay ACR instead of diode isolator.

AP

[crushrus]

There’s a one way selenoid between the front and back batteries, it’s controlled by a live wire in the van. When it’s running. It trips the selonoid and charges the rear. I suppose I could disconnect rear and see if it makes a difference but again, the randomness with which this happens makes it super confusing. It’ll sit for a week or two and start no problem, or it’ll be dead the next day.

Also, the whole system with the second battery has been in place for a year, never an issue. It certainly ‘could’ be that, but I don’t think it’s likely.

[SafariSoGood]

Did you resolve this? I had the same problem recently with a 99 sable wagon. In that case it was the alarm system. (Of course a mechanic sold us a new battery before we learned to do our own analysis.)

We did a parasitic drain test -just looked at the draw on the battery as we pulled each fuse. I'm no expert but I think even if you have a short somewhere you can narrow down to the circuit.

[WE7X]

Sorry, I just found your note.
Did you find the culprit to your battery drain problem?
If not, PM me, and we can go from there. I have quite a lot of experience in automotive and industrial electrical stuff ( made my living at it). What year is the van?