Has noting to do with the transfer switch. Modern alternators wait for the voltage to stabilize so as not to burn themselves out. They send current in bursts to bring the battery voltage up in a controlled fashion. Once the load is safe for it, it will run in a state to maintain the batteries. Alternators are not designed to charge batteries, just maintain them. I'm not saying they don't charge batteries, just that they will last a lot longer if they are only required to maintain them.
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Jeff and Elaine
2011 Berkshire 390QS
2 Lab Dogs-Eros and Star