The car is being used now as a daily car so this means for me a minimum of 3 times per week for my long commute of 120miles each day. For the last two days before the below mentioned incident I used a fm Bluetooth transmitter and apparently the cigarette lighter socket is not very good so the transmitter was going on and off till I inserted it at an inclination. After 30’ of driving the ngt1 switched off on its own and restarted. Everything else worked ok and the ngt1 didn’t restarted any more times. incident : Few days ago, I turned key in position 2 (I always turn it to position 2 and after 3-4 secs I will start the engine) and brake failure came on the dash saying that I have to depress the brake pedal completely and then was saying to start the engine. Engine didn’t start so I guessed battery failure. I switched off and on and I checked with the reset button the battery voltage which turned to be 8.4V. Again the brake message came on and then was stating to start the engine. With a quick look I read that Merc used to install AGM as oem but after few years with a service bulletin or something equivalent they recommended the classic lead acid. My car had already an aftermarket lead acid one of 90Ah (with no indication for the date it was installed on the car) so I proceeded with a yuasa 100Ah (from 7zip I found that the car should have 100Ah batt). I also found wet the area next to the battery so I dropped a microfiber to check in a week’s time. Maybe there is a leakage from the right rear light seals? Or maybe from under the plastic cover trim on top of the rear wing and below the boot lid? The rubber seal of the boot lid is ok with no wear and tear at its length. I have read online that generally speaking the CLSs are battery eaters. Because of my long commute I would say that the battery would be charged properly. From Torque pro or from reset button in hidden menu I have seen that the batt is 14.1V-14.3V when driving so I don’t believe its an alternator issue. I don’t dare to use the fm transmitter at the moment till I will be sure that battery and alternator are working fine. What do you think? Till the end of this week I will have a icarsoft mb2 to have a further look. PS: previous owner informed me back in April that he replaced the aux battery under the bonnet and with small research online i saw that if this had an issue the engine will be able to start etc.