1989 Toyota Camry warning lights

Am trying to get 250000 on this car. First car I am able to do this with. Was driving along tonight and the charging and brake warning lights on the dash came on simultaneously. Car running fine, brakes working fine. Lights stayed on for about another 20 minutes and while at a light the cooling fans came on and the lights went off. Continued to destination. Later started car drove for about 30 minutes both lights came on again. Car still running fine at night with headlights etc still on. Lights stayed on till I got home. Replaced serpentine belt last night and don't think it has anything to do with this. Tension seems adaquate. What do you think?