Battery indicator light details?

Hello all, first post after lurking for some time. I'm glad to be joining you! I have a question regarding the battery light. So, my battery light comes on before I start my 2006 Diesel Dodge Sprinter. I just purchased the vehicle and drove it 500 miles and then it had a little trouble starting (churning like the battery was dead) but did start. I'm suspecting the battery is dead as I think the vehicle was waiting to be sold for about 2-3 months (i.e. not driven much) or the alternator is dying as I've read the alternator can discharge your battery when it's dying. Any theories? need more info? Thanks everyone!

I believe it's normal for the battery light to come on before you start it. Are you in a cold place? I think the alternator probably doesn't discharge the battery, rather it doesn't charge the battery, leaving it low. I think others will chip in with more expertise, but more details would hurt, especially about the hard starting session.

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The only thing you can/should do is measure the system with a voltmeter.
With the engine off, the battery should be at or above 12.4 volts.
When the engine's running the alternator should be lifting that to 13.6 to 14.2 (the higher voltage is soon after starting, then it drops to the lower voltage as the battery gets recharged from the starting load).

If you don't see it rise above 13v within 20 seconds after starting, either the alternator isn't working properly, or the battery has a shorted cell and simply cannot be dragged any higher. (a shorted cell would put the "engine off" battery down below 11v)

A gadget like a ScanGauge plugged into the OBD port has "real time" voltage readings available, you can also buy voltmeters that plug directly into the dashboard's 12v socket.

--dick