Battery light

[mauser]

Have a 2001 F250 7.3L ... Last year this month the battery light came on intermittent.. had it check out and was told - system working properly, just needed two new batteries. That was close to 3 bills with diagnostics and batteries. Doing the same thing this year this month... gauges indicating system charging alright, no drop on gauge (turning lights on and off, reeving engine etc) stays around the 14amp range if I were to guess and does not fluctuate. When I increase speed quickly, the light goes out but comes back on when engine RPM starts to level out. I am up here in SW Pennsylvania (cold)... could one of the batteries (or both) have gone bad already, or going bad within this past year? I know it's possible.. the batteries are Interstate. Being the weekend it's difficult to run a diagnostic on the system with no one open, and a load tester will only let me know if the battery had a bad cell or can not hold a load... Truck starts okay, need to have it plugged in over night in cold WX.. and I know it needs glow plugs and GPR... any help would be appreciated...