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I have a 2006 Honda Civic SI.

It was slow to crank when starting up, and while driving, electrical systems progressively got worse (radio would turn off and on, power steering would stop, and then car would eventually just turn off completely and turn back on).

The symptoms were worse when there was a heavy electric load (windshield wipers and lights on, etc.)

Because it was having issues while running, I assumed this would make it an alternator problem. With my multimeter, the battery tested at 12.6V while off, and between 13V and 14V while on.

At Autozone, their tester said it had a bad cell.

Once I replaced the battery, all the symptoms were gone. What did the battery have anything to do with the car having those symptoms while turned on?

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I don't know what they call it now, but the way it was explained to me was the battery has what is called a "surface charge". It's enough of a charge in the "bad" cell for it to pass electricity, but not enough to keep things going. The single cell discharges faster than it can recharge. This means, when this single cell is depleted, the battery as a whole cannot keep up and all of your electrically powered equipment will start to fail (well, not work, anyway). This is a "weakest link" type of situation.

Everything you stated about your situation tells me the Autozone worker is spot on with their analysis. I would have given you the exact same resolution.

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  • Makes sense. So all the electrical systems are drawing power directly from the battery still (while the battery is just being charged by the alternator)? I had assumed that the electrical systems somehow drew their power through direct connection to the alternator and left the battery alone while the car is turned on.
    – Josh Beam
    Sep 24, 2014 at 16:56
  • @JoshBeam ... It is my understanding that is the way it works, draws from the battery and is replaced from the alternator. I found out about this the hard way way back when my first car's battery did the same thing. It left me stranded a couple of times. My Dad told me to put a new battery in ... never had another problem with it again.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Sep 24, 2014 at 17:47
  • Once the engine has started, its electrical loads are fed by the alternator up to its output capacity. A bad cell in the battery would act something like a resistor and not allow a good circuit.
    – Allan Osborne
    Sep 24, 2014 at 18:34
  • The point is... in most systems it's all one system. It's not so much that everything draws power from the battery specifically, but that everything is one big circuit.
    – maplemale
    Nov 9, 2015 at 16:26
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Batteries have what is called a surface charge, which is probably the reason yours tested 12.6V -- you should wait several hours at room temperature prior to testing the voltage of the battery to compare against the 12.6V/12.7V standard.

The reason you had intermittent electrical issues might be related to the fact that battery was consuming a lot of power (maybe indeed related to a shorted cell, as they call it). The alternator is generally not designed to produce enough power when the car is at its idle and all accessories are on (especially some power hungry ones like heated seats and AC), so, that is likely where your symptoms were at its worse (perhaps also complicated by a weak alternator in addition to the old battery).

BTW, prior to discarding an old maintenance-free battery, you might want to check the water level within, add some distilled water, to see if the situation could be improved. However, it's probably unlikely to help if one of the cells in your battery has indeed developed a short.

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