What is the best voltage for charging a 12V lead-acid battery?

In the context of charging a 12V lead-acid battery, the optimal voltage is indeed around 14.1V. Lead-acid batteries require a higher voltage than their nominal rating to effectively charge them. When charging, the voltage needs to be increased to overcome the internal resistance of the battery and to ensure efficient charging.

At 14.1V, the battery enters a stage known as the bulk charging phase, where it can absorb the maximum amount of current safely. This higher voltage helps to fully charge the battery and brings it up to its full capacity. Once the battery reaches a certain state of charge, the charging voltage may need to be reduced to prevent overcharging and to maintain battery health.

The other voltage options, such as 12V, 11.8V, and 12.3V, are too low for effective charging of a 12V lead-acid battery. These voltages would not provide enough potential to lead to adequate charging, as they fall below the battery's nominal voltage and do not account for the necessary charging characteristics. Using these lower voltages could result in insufficient charging and lead to sulfation and reduced battery lifespan.