random battery drain - Toyota Nation Forum : Toyota Car and Truck Forums

skynet1988 · 10-03-2010, 01:16 PM

For the past two months, my car has been randomly having a hard time starting. The alternator does put out 14v so I know that the charging system is working. The car will be slow to crank and the battery only reads 10v but recharges fine. I had the battery load tested and the charging system checked at sears and it all came out fine. any ideas? Thanks!

***MR2Jedi*** · 10-03-2010, 01:26 PM

Disconnect your negative battery cable. Use a test light between the Negative battery post and the negative cable. If it lights up, you have a short which may be slowly draining your battery.
If not, it may be a starter problem.

skynet1988 · 10-03-2010, 01:29 PM

OK, but wouldn't it glow anyway because of the car alarm and the power used to keep the memory alive for the car radio and the ECU?

TedL · 10-03-2010, 03:51 PM

This answer is simply wrong. When the ECU volatile memory and radio volatile memory and clock (any any other parasitic draws) are receiving power from the battery, there will be current flow back to the battery, via the negative cable. That is the nature of DC current. There is no other path for it to follow.

Better to use a VOA meter between the cable & terminal, and measure the parasitic amperage. Remove fuses that should show such draw, and see what happens.

***MR2Jedi*** · 10-03-2010, 05:32 PM

I shoulda been more specific. I use a Multi meter and it will read as negative polarity voltage .
On a ordinary test light, I didn't think it would light at all, unless there was a short.
Is that not correct?

TedL · 10-03-2010, 06:27 PM

Depends what you're using for a test light, whether the normal "always on" current will make it glow.

The simple and accurate test for parasitic loss is amperage. VOA meters are $2.50 at HF. Everyone should have a couple. Normal seems somewhere in the 50-100 milliamp range, but I'm not comfortable giving that as a spec. Could be as simple as a trunk or glove box light not turning off, or something plugged into an always on source.

***MR2Jedi*** · 10-03-2010, 07:12 PM

I see.
I was refering to those simple test lights-pointed tip probe with a light and a ground wire.
.

Jigg007 · 10-06-2010, 04:24 PM

Whats the time between difficult starts? Within the same day? If thats true I'd say you have a pretty big drain problem. You commented on the battery testing OK, but knowing the age may be helpful. I've had batteries for only a year that would go bad.

And by go bad I mean a cracked cell or similar. It'll throw you for a loop, because it will test fine for a short time, but under a few seconds of load the batteries output capacity drops dramatically.

However, if your battery stays at 10 volts while cranking over the engine, I would say your problem is elsewhere. Possibly correded terminals on the battery or starter.

I had one battery, cheap one, charging voltage was 14V, engine off was 12.2 volts, but had a problem starting. Load test the battery, one time, two time, all fine. Go to test it a third time, voltage is appropiate at 10-11 volts, then all of a sudden drops to 7 volts. And it was 2 months out of warrenty, curses!

If you do replace your battery, do yourself a favor and opt for an AGM type. It'll handle drains better atleast.

pphhss · 10-07-2010, 06:40 AM

You say it's random. Are you sure your doors are being closed tight each time. I've noticed on my '96 that the door courtesy light stays on if the door isn't shut tight.