[quote name='ds968' timestamp='1346026997' post='131676']
Usually what I notice is that the battery voltage on starts is at least half of a bar higher ( closer to 14 ) than when driving when it dips a bit..
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That is because of the voltage regulator which adjusts the voltage to the battery depending on the state of its charge. A typical car alternator puts out about 14.5 or 14.7 volts (or something like that). When starting the car, the battery gets drained quite a bit to provide power to the starter. So initially after start the regulator allows high voltage to recharge the battery faster. Later after driving a bit the battery has recharged, so there is no need for a higher voltage so the voltage regulator cuts the alternator output to 12.5 or 12.1 or some such number. Providing the 14.5 volts to a charged battery may damage it, or I guess reduce its life.
The gauge is an indicator of the charging voltage, not the stand alone battery voltage. If you let your car sit for some time, take a measurement of the battery voltage before starting the car. You might see it at 11.8 or 11.5 volts. That is not a problem for the starter, since the important thing for the starter is the AMPS (like we see in battery specs "amp-hours"). All of the other electronics are of course designed to operate correctly within some voltage range -- I have no idea what that might be, but think of the starter and electronics all working and happy within a range of 10-16 volts (for example). I have no idea what the spec is on the fuel injector, but the point above was very interesting, that the computer adjust for slight variations in voltage. As a silly example I just checked the spec on my radio, it is happy at any voltage between 10.8 - 15.1 volts.
Roland
