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The Terminator
Engine/Tuning
Low battery voltage under load--battery or alternator at fault?
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<blockquote data-quote="TheFleshRocket" data-source="post: 15692551" data-attributes="member: 48535"><p>Technically speaking, 12.6V at rest is considered a fully charged battery. When a battery has just finished charging (or when you just shut off your car after driving for a bit), the battery will typically have a "surface charge" so its voltage will be in the upper 12s or possibly even low 13s, and it takes the battery a while (couple hours, perhaps) for its voltage to drop down to its true resting voltage. The battery in my Cobra shows mid-12s immediately after being charged, and its resting voltage is usually in the low-12V range, so it's definitely not performing optimally. </p><p></p><p>This thread explains surface charge (and quite a bit of other battery-related stuff) in pretty good detail: <a href="https://mechanics.stackexchange.com/questions/44197/what-is-surface-charge-and-how-does-it-affect-battery-testing" target="_blank">https://mechanics.stackexchange.com/questions/44197/what-is-surface-charge-and-how-does-it-affect-battery-testing</a></p><p></p><p>My primary question is whether a weak battery can cause low voltage under load, or whether the alternator should put out enough juice to compensate for a weak battery.</p></blockquote><p></p>
[QUOTE="TheFleshRocket, post: 15692551, member: 48535"] Technically speaking, 12.6V at rest is considered a fully charged battery. When a battery has just finished charging (or when you just shut off your car after driving for a bit), the battery will typically have a "surface charge" so its voltage will be in the upper 12s or possibly even low 13s, and it takes the battery a while (couple hours, perhaps) for its voltage to drop down to its true resting voltage. The battery in my Cobra shows mid-12s immediately after being charged, and its resting voltage is usually in the low-12V range, so it's definitely not performing optimally. This thread explains surface charge (and quite a bit of other battery-related stuff) in pretty good detail: [URL]https://mechanics.stackexchange.com/questions/44197/what-is-surface-charge-and-how-does-it-affect-battery-testing[/URL] My primary question is whether a weak battery can cause low voltage under load, or whether the alternator should put out enough juice to compensate for a weak battery. [/QUOTE]
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Low battery voltage under load--battery or alternator at fault?
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