"Veggie" bravely wrote to "All" (11 Oct 05 23:19:43)
--- on the heady topic of "charging a fully discharged car lead acid battery"

Ve From: Veggie
Ve Xref: core-easynews sci.electronics.repair:344843

Ve I have a car with a battery that is completely discharged (accessory
Ve left on for over 24 hours). Read 0 volts.

Ve What is the best way to remedy this?

Ve a) jump start - it seems to not be a good option as it dumps high
Ve current into the dead battery. If you're on the road somewhere, sure,
Ve you need to get going but jump starting seems to be undesirable.

Ve b) put it on a battery charger, one of those 5/10/25 amp ones. If so,
Ve which rate is the best for a completely flat battery?

Ve There seems to be a lot said about sulfate build up on batteries. It
Ve seems to be an unsettled subject on the Net, as many say one thing but
Ve an equal number refute it. One claim in interesting to me- that
Ve leaving a lead acid battery in flat condition for a long time caused
Ve sulfate build up. Is this true, and what is a "long time"? Are we
Ve talking days, weeks, or months?


Charge it at a current rate as high as possible but that doesn't cause
rapid dissociation of the electrolyte (hydrogen outgassing). One might
start at only a mere 1 ampere and work up from there as the terminal
voltage reaches a nominal minimum 1.75V per cell (depending on
temperature).

Mind that if the battery measures zero volts under load that it may
still exibit 12 volts open circuit and not accept any charge at all.
In this case one might try raising the charging voltage until it
begins to accept a charge. Then continue the charging process in the
usual contolled manner. If it won't accept a charge then chuck it.

A*s*i*m*o*v

.... Real techs don't lick nine-volt batteries!