1997 Toyota Avalon Constant battery drain

After purchasing the car, iI brought new battery to replace the old one, after three months I notice every time my wife drive to her place of work and her way back mostly about parking to open gate to drive in, getting back to start the car it will not start. Sometime it will be while trying to start the car in the morning it will not start. I don't know what to do as most mechanic or battery charger around here in Lagos Nigeria kept saying different things. I notice since iIbrought the car as used car, the check on the dash board is on. Also track of keep blinking, Abs also on the dash board when the engine is on. Please kindly help on ways to solve this