Fact: Alternators are not designed to charge dead batteries. 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.
Similarly, can alternator charge two batteries?
A car alternator will be more than capable of charging two batteries. The first is if both batteries are low on charge then that would be too much for the alternator, but if only one is low then it would be fine. The second thing is linking the batteries will cause more problems.
How long does it take a car alternator to charge the battery?
Basically, at idle you can probably get 80 amps out of your alternator. You can charge a flat battery to 80 percent full in about 2 hours, so long as you alternator can manage produce around 14 volts at the battery terminals this whole time.
Can you charge two batteries with one charger?
Two Batteries in Parallel, One Charger. Batteries connected in series strings can also be recharged by a single charger having the same nominal charging voltage output as the nominal battery pack voltage. In Figure 8, a single 24-volt charger is connected to a 24-volt battery pack.