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2013 Subaru BRZ
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I know this is basically about:

1. The rated Ah value of our batteries and how would the Ah value vary at different temperature.
2. How much of the battery is charged during normal operation, 90%?
3. The minimum capacity of the battery left required to turn over the engine.
4. The currency that runs through the battery when key is on 'ACC' or 'ON' when we just play music at normal loudness.

But I have no idea about what the common values for all four questions should be. Anybody can help?

PS. I know key should be on 'ACC', not 'ON'. But I am just curious.
 

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Someone with more knowledge could answer this...but I can put my .02 in.


Too much varible. The car battery should be ideally near full charge. Listening to music shouldn't be too demanding, but depending your audio setup, it could vary the most. A basic 4/6 speaker setup in the Camry without an external amp should be the most efficient. Premium setup such as the JBL amp might consume more. Custom systems with a full blown external 4 channel/5 channel amp may use a lot more power.

For what it is worth, if the battery is in good shape, you can probably listen to over a few hours with the Camry base or premium stereo without issue (although I'd probably not b/c I'll get OCD to use a batt tender after). I've had times when the Battery was going bad where I could get about 30/45 minutes before I couldn't crank.
 

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Token Aussie
1998 AE102, 2018 ZRE182
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2,454 Posts
I know this is basically about:

1. The rated Ah value of our batteries and how would the Ah value vary at different temperature.
2. How much of the battery is charged during normal operation, 90%?
3. The minimum capacity of the battery left required to turn over the engine.
4. The currency that runs through the battery when key is on 'ACC' or 'ON' when we just play music at normal loudness.

But I have no idea about what the common values for all four questions should be. Anybody can help?

PS. I know key should be on 'ACC', not 'ON'. But I am just curious.
A rough guide can be found by looking at your battery's spec sheet, in particular the Reserve Capacity and Amp-Hour ratings. Reserve Capacity is the number of minutes that your battery can sustain a 25A load @ 70F and maintain a voltage greater than 10.5V (basically deemed to be an average load of a running car with a failed alternator). Amp-Hour rating is similar except the rating is in amp-hours, thus you divide this by your expected load current (as a guide your average car stereo without external amplifier won't be pulling more than 10-15A, as that is what the head-unit fuse will be rated to) to get the time before the battery drops below 10.5V. Note that the 10.5V figure is basically the lowest voltage that your average 12V lead-acid car battery can put out and still be moderately effective, discharge it any lower and there's no guarantee that it is recoverable (and 10.5V may not be enough to start the car in the first place) and a lot of the car electrics won't work properly at that low a voltage anyway.

It's a safe bet that you'll be able to run your stereo for a couple of hours or so assuming the battery is fully charged and you're not running a sound-off setup. For instance, the Century battery in my Camry is rated at 620CCA, 120 RC and 70 AH, so it can run a 25A load for 2 hours (120 minutes) or a 10A load for 7 hours (but no guarantee that it'll be able to start after that)
 

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short-throw dipstick
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Lol my crappy run-down Interstate battery lasted 30 minutes waiting for somebody in a parking lot. Starts the car just fine but that long on radio at low volume and no-start.

EDIT: Should have mentioned, it came with the car (depleted at that time, think it was permanently damaged), and has a fair bit of sulfate residue that builds up after every cleaning.
 

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Try popping the battery caps and filling with distilled water when the battery is cold (in morning before starting). Have saved a few this way, and a gallon of distilled water is about $.85 at walmart
 

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short-throw dipstick
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Try popping the battery caps and filling with distilled water when the battery is cold (in morning before starting). Have saved a few this way, and a gallon of distilled water is about $.85 at walmart
I did :smile:...that was a fluke, this car's always running anyway, commuting back and forth. Friend's going to buy it, new battery is on her.
 
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