Posted: Aug 01, 2012
Fact: Alternators are not designed to charge dead batteries
Jumper cables can be a lifesaver, literally! However, when you use jumper cables to start your vehicle, you are placing a tremendous strain on your vehicle's alternator and battery. That is why we recommend fully-charging deeply-discharged batteries with a battery charger as soon as possible.
We're not alone in that thinking either. Look at the first installation instruction on this alternator box, which is printed in bold text, for additional emphasis- "CHARGE BATTERY - (12.6 Volts min) The alternator isn't designed to charge a dead battery. Premature alternator failure can occur and may Void Your Warranty."
Alternator manufacturers know the same things about alternators that we do- they are designed to maintain batteries that are near a full state of charge, not recharge deeply-discharged batteries. We post this on message boards all the time, but there are still folks who are convinced their alternators are designed to recharge deeply-discharged batteries. We know this, because they call our tech support lines on a regular basis, because their battery keeps getting deeply-discharged (it is actually just staying deeply-discharged). The alternator manufacturers also get calls from these folks, because they've burned up their alternators, trying to recharge deeply-discharged batteries.
Does this mean you should never use jumper cables to start your vehicle? Absolutely not! We carry them in all of our vehicles, in case of an emergency. However, when jumper cables are needed, be sure to get the battery fully-charged with a battery charger as soon as possible.
As the alternator instructions suggest, our REDTOP® batteries are fully-charged at about 12.6-12.8 volts and our YELLOWTOP® and BLUETOP® batteries are fully-charged at about 13.0-13.2 volts. Failing to do this can lead to a cycle of dead batteries and jump-starts, until either the battery (expensive) or alternator (really expensive) fails.