12 V Battery Monitor

I was looking around for an LED panel to install in my Leaf to monitor the 12v battery and I cam across the INNOVA 3721 Battery and Charging System Monitor https://www.amazon.com/gp/product/B000EVWDU0/ref=od_aui_detailpages00?ie=UTF8&psc=1 on Amazon. This plugs into the 12v receptacle (aka cigarette lighter) and for $10 looks like it will the trick. I am getting it Saturday and so I'll post my impressions.

Not going to be very useful.

When LEAF is OFF, the 12V accessory plug is disconnected.

When LEAF is on the LEAF DC to DC maintains 12V on the 12V battery (or more depending how much power was used from it).

So the device will not provide useful info on the 12V battery.

You can do some evaluation measuring voltage after LEAF has been OFF for a while.
But you cannot do through accessory port.
But voltage testing is very imprecise for evaluating 12V battery.

Real check of 12V battery capacity requires a real battery tester.
Auto Zone, Advance Auto, Pep Boys, etc. will do for free.

Just tried it with the car in the driveway - if I start the Leaf without my foot on the brake, the battery registers 12.55 volts; when I start the car with my foot on the brake, it bounces around from 13 - 14 volts. The directions state that monitoring the battery without starting the car gives the state of the battery while monitoring with the car running monitors the charging system.

I'm sure I will get a lower reading in the morning after the battery sits overnight.

joeriv said:

Just tried it with the car in the driveway - if I start the Leaf without my foot on the brake, the battery registers 12.55 volts; when I start the car with my foot on the brake, it bounces around from 13 - 14 volts. The directions state that monitoring the battery without starting the car gives the state of the battery while monitoring with the car running monitors the charging system.

I'm sure I will get a lower reading in the morning after the battery sits overnight.

Click to expand...

No need to wait for morning, just wait a few minutes after "run mode" when the charging system stops the top off

joeriv said:

Just tried it with the car in the driveway - if I start the Leaf without my foot on the brake, the battery registers 12.55 volts;...

Click to expand...

That's a decent result for a single press (ACC). Mine started out at about 12.59V and then slowly dropped through 12.55 to about 12.50 before I got bored of waiting. Then I pressed the button a second time (ON). In that mode, the voltage dropped down to about 12.2V with no fans running. I was able to get it to drop down below 12.0V (a warning light and chime occurred) by putting down two windows simultaneously, and then it rose back up close to 12.2V.

joeriv said:

...when I start the car with my foot on the brake, it bounces around from 13 - 14 volts.

Click to expand...

More specifically, it rises quickly to 14.0V, then it goes up to 14.4V, finally, it drops down to 13.1V.

joeriv said:

J The directions state that monitoring the battery without starting the car gives the state of the battery while monitoring with the car running monitors the charging system.

Click to expand...

That might be the case if the 12v outlet was always powered (most older cars, some newer cars have a designated always "on" outlet as well), however on the Leaf it is only powered when on, so, will not tell you much about the battery...