Quote:
Originally Posted by reignofchaos You don't need to reach 9.6V to reduce the life of a battery. If the battery has reached 9.6V, its as good as gone. Actually anything below 45-50% discharge of an SMF battery will reduce its life span drastically. At 50% charge, the voltage will be down to 12.1V or so. |
* 12.1V at 50% charge is OPEN CIRCUIT voltage - no load connected. One cannot discuss in Open Circuit terms for practical usage, since one never measures Open Circuit. Even the battery-wala measuring the voltage (with his charging box) after taking out battery does it with a nominal load, since otherwise they cannot account for / detect "cell failure"
* The "nominal 12V" is actually 12.66V at 100% charge, measured at open circuit at 20C. Open-circuit voltage is measured 12 hours after charging to allow surface charge to dissipate and enable a more accurate reading
* The voltage at 0% charge is 11.7V, again measured Open Circuit at 20C
* Since OC voltage of Lead Acid batteries is negative temperature coefficient (-0.022V/DegC), the voltage reading will be lesser at higher temperatures
* ALL automotive electronics is designed to operate reliably in the range 12V +/- 20%, i.e. 9.6-14.4V, since operational conditions are never "open circuit". Different loads can pull down 12V line to as low as 9.6V, but the voltage recovers once the load reduces
* "Deep discharge" affecting the life of the battery would be over-stressing it. An SMF battery usually has a life of 400 discharge cycles (down to 0%). The usual charge range in mixed (day + night) usage is 40-100%
* Very few people allow the battery to go to deep discharge state. No sane driver does it deliberately. Oversight may cause it, like forgetting to switch off parking lights (headlights usually go off when key is removed), or interior or engine bay light. BUT this is a rare happening, if at all it happens. Under such circumstances, "life" of battery is not a big concern
* If the driver is listening to the radio at a low volume (that's what they do when parked in office / basement parking), he can do it for a few hours and still the charge condition will not go below 40%. The starter will be able to crank the engine even at 10% charge, albeit it will be hard labour and one can hear it. Modern controlled-injection engines are able to start even in that condition, and charge reaches 30-40% in 10 minutes driving
It will be a different story if he is tripping away listening to item numbers at a loud volume, especially if the owner has fitted good ICE. Then he can discharge the battery in 2-3 hours, and will face the wrath of the owner when it is time to go home. Some drivers are indulgent, but very few are that stupid.