Random low battery issue - Toyota Nation Forum : Toyota Car and Truck Forums

Miranthis · 03-25-2010, 08:34 PM

2005 Camry SE I4. battery is 18 months old, alternator is a little newer. Last week or so it has been slow to crank in the mornings and if I don't drive it over a full work day. I checked voltage when I get home (after 25 minute, mainly highway drive) and it is 12.9V or so. No load voltage is between 13 and 14 V, so alternator/generator should be OK. I pulled - cable and let it sit 15 minutes and the ammeter shows a parasitic load of 0.09 - 0.1 mA. Is that a sign of a short or do I just have a bad battery? Thoughts?

And yes, I DID search and I find that folks are very sloppy about units. 0.2 A is not the same as 0.2 mA or 0.2 microA.

Thanks in advance!

Jeff

gdanaher · 03-25-2010, 10:12 PM

The car has a clock and a radio memory that will draw just a trickle. That isn't the problem. Check the voltage as you have someone else crank the starter and see how low the voltage drops and how quickly it recovers. An 18 mo battery could easily be bad. I had a battery lose cells on a new car that was 30 days old and a battery last over 7 years. Age has little to do with it.

***Yazovets*** · 03-25-2010, 11:43 PM

Well my first battery lived for just under 2 years. The engine would crank slower and then the battery started to systematically leave me stranded, unable to start the engine. I boosted that one about 3 or 4 times before installing a new battery (which solved all problems).

Miranthis · 03-26-2010, 10:17 AM

voltage dropped over the night from 12.79V to 12.60V It started ok, so the voltage must be lower when it cranks slowly. My guess is battery, but I just wondered how much the 'normal' draw was for computer, clock etc. I will just take it to the place I bought the battery and see what we can do.

Thanks!

Jeff

gdanaher · 03-26-2010, 11:36 AM

Check the connections on the battery terminals to verify that they are clean. Keep your volt meter handy and if it cranks slowly again, jump out and check it. Generally a battery is good or bad with little in between. In fact the battery will suffer a prolonged death beginning the day it is made, but it usually isn't noticed until that fateful, cold, morning.

The7 · 03-26-2010, 12:44 PM

Quote:

Originally Posted by Miranthis

I pulled - cable and let it sit 15 minutes and the ammeter shows a parasitic load of 0.09 - 0.1 mA.

0.1 mA will take 10000 hr (416 days) to drain 1 AH.

Most car batteries have 35-50 AH.

Don't think this small drain current will cause any starting problem for a healthy battery.

The7 · 03-26-2010, 07:10 PM

Most car batteries are charged using "constant voltage" technique.
For 12 V battery, the nominal charging voltage is 13.2 to 14.4V.
A healthy alternator would have about 13V at idle and 14V for higher rpm.
Most alternators have maximum output 60-90A.
The cranking (start) current could be 300 - 600 A and last about 2-5 seconds.
The cranking voltage could be as low as 9 V.

The (worst case) cranking AH could be 600x5/3600 = 0.84 AH (less than 1AH for one crank).
For a charging rate of 30A, it takes 100 sec (less than 2 min) to top up the cranking AH.

IMO.
When to replace car battery?
Most car batteries should have a life > 5 years.
If the battery requires "external" charging in order to crank the car properly, I would consider to replace it when it happens to me the second times.