At least since InfluxDB server v1.8.0 precision in client cannot be set to micro seconds. Using "u", validation fails in NewBatchPoints(), using "us", Write() fails:

precision 'u' failed: NewBatchPoints failed: time: unknown unit u in duration 1u
precision 'us' failed: Write failed: {"error":"invalid precision \"us\" (use n, u, ms, s, m or h)"}

In influxdata/influxdb@275b02e a verification rejecting write requests with precision "us" was added.