Charging System light on when car is stopped?

A couple of days ago my charging systems light started coming on, but only while I was stopped in traffic or a red light for longer than 10 seconds. Once I started driving again the light went off.

I have a 2005 Ford Focus and I've never seen this happen before.

I'm not sure if this is related, but about a week ago I started using a Progressive Snapshot device, which plugs into the diagnostic port of the car and monitors driving. This device sometimes turns off and then back on when my car is stopped for a minute or so.

Are these two related at all or is there something more serious wrong with my car?

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