Quote:
Originally Posted by Daox
I'm having some problems with battery voltage dropping way too low in my morning commute to work with headlights on. . . .
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So I take it you prefer to coast with the engine off and that is why your alternator does not produce enough electricity for the 12 starter battery to run your accessories. . . .
The technically correct answer is to have one 'high discharge battery,' with the high cranking amps needed to start the car and a second, deep discharge battery to handle your 12 VDC load. Each is optimized for their specific missions and trying to use a 'starter' battery for deep discharge just makes it fail that much sooner.
One exception might be the Odyssey battery. They appear to have done some serious engineering in their batteries and claim to have both starter and deep discharge capabilities. I put one in my Prius, $170, based upon avoidance of a vent tube and their reported specifications. They have an 8-10 year projected life.
Do you have a measurement of how much current is drawn when your engine is off? This pretty well sizes the type of deep discharge battery needed. Although splitting the 12 V system is not a trivial task, it makes it easier to build the battery system you need. The 12V starter battery gets charged from the 12V deep discharge system using a current limited, DC-to-DC converter and/or a second alternator.
Have you looked at after-market options to reduce your electrical load? For example, LED rear lights or discharge head lights? Are there any other electrical loads to remove?
As for trying to get more use out of marginal starter batteries ... GOOD LUCK!
When a cell fails in one of them, that will be pretty much it. The question being do you want that to happen on the road?
GOOD LUCK!
Bob Wilson