Ongoing Battery discharge problem
 

Hi
My car would not start the other day after being parked for 4 days, I did start it with a trickle starter "hope that is the correct name" at the last day I drove it before that I had forgotten my iphone on the car charger for 9 hours on the car charger while at work, but the car started normally that day.
After three days the car would not start so I took it to the local MB dealer, they told me that both seat sensors are faulty and draining the battery. So they replaced the drivers seat module and disconnected the sensor of the passenger seat because they had to order that unit first for me.
I took the car and drove back home, drove the car the next day to work and back home, and yesterday I tried to start it and it would not start. The battery is dead again, I called the dealer and they told me I would have to replace the battery, but to be honest I am not sure about it and I do not trust their judgement anymore. For one, why would both seat module go bad at one time, and for two why would the battery suddenly discharge at this rapid rate even if nothing is abnormally discharging it. Could it be that the battery was not fully charged yet ? How much should I drive to fully charge it ? Could the two first discharges have damaged the battery ?
Thanks