Brand new Optima Battery dead in the morning

I think you are correct in that something is drawing current. Seems I remember a thread of somebody having a similar issue not long ago on here. Do not remember much about it though, sorry. Hate it when that happens cause I can't help but think I want my old battery back and my $200!
TomK

 

The person who told you they can't test the Optima because it is a hybrid battery, to put it nicely, is wrong.

Something may have happened to the battery -- or maybe it it fine, but I'd get it tested first and go from there.

 

If autozone can't test the battery, I would just return it for a refund and buy another one elsewhere. A new battery should not be worse than the old one you tossed out. Your car still could be drawing current but that battery needs to go back.

 

You won't know, until you connect an ammeter in series with a good 12V battery installed into the Prius, and see what the quiescent current draw is when the car is IG-OFF and all doors are closed. The trunk light needs to be disconnected or the light switch needs to be manually put into the OFF position. The current draw should be ~0.03A.

When the Prius is READY, you should measure ~13.8V across the battery. If not, the DC/DC converter within the inverter has a problem.

 

Get an Amprobe and clip it on one of the battery cables. It will read the current draw without having to disconnect a cable.

 

Amprobes (or other clamp meters) are handy, but the inexpensive ones are AC-only so they won't be of any use to measure DC. Climbing up the price scale you can get into Hall-effect clamps that will measure DC (e.g. Amprobe ACDC-100, etc.) but the thing is, that clamp's accuracy spec is something like 1.5% of the full scale range plus or minus four units in the least-digit place. That means for measuring something like the 30 milliamp quiescent current in a Prius, the value you're trying to measure is invisible to the instrument.

Something like a Fluke i30 could work - will read a max of 30 A and read down to 5 mA. But at $475 you'd probably want to have a regular reason to need it.

-Chap

 

Make the Prius IG-OFF. Turn off the cabin lights and close all doors. Remove the trunk light bulb or place something into the trunk light switch to keep the light turned off.

Hook up an ammeter in series with the 12V battery so you can read quiescent current draw. After the car settles down, the drain should be 0.03A or so.

If much more, then you have to start pulling fuses to see what circuit is causing the excess drain. Maybe you have a stuck relay.

Refer to techinfo.toyota.com to obtain an electrical wiring diagram for your model year, which will help you to more intelligently figure out which fuses to start with.

As a separate issue, you should put a charger on the 12V battery to bring it back up to full charge, while you are trying to figure out what is draining the battery.

 

You can buy an inexpensive digital multimeter pretty much anywhere, including at auto parts stores, home repair places like Home Depot, hardware stores, on Amazon.com, etc. Usually a multimeter will have an ammeter function that can read current up to 10A.

Given that 10A limitation, you do not want to leave the ammeter connected when you want to make the Prius IG-ON or READY, as the current surge associated with powering up the car (30A or more) will blow the ammeter's fuse.

If you want to buy a clamp-on DC ammeter, that will be more costly and as previously pointed out, you need a good one to read very low current levels. So I think you would be better off with a digital multimeter which you can then use for a variety of household purposes.

I have several digital multimeters but my favorite is my Fluke 87. However that probably goes beyond your requirements and cost budget, if you are a casual user.

 

Well, I hope you will fully-charge the 12V battery now because 11.4V is near-dead and at this rate you'll have another no-start situation to deal with. The battery voltage should be much higher, like 12.7V to 12.9V after surface charge has dissipated.