Preface: I drive a 2004 Peugeot 206, manual
On the motorway the other night, one of my tires blew out. I managed to pull over and change to the spare wheel in about 30 minutes (having never changed a tire before! Lesson learned!) but because it was dark I decided to leave the dipped headlights on in addition to the hazard warning lights. Additionally, I stupidly left the sat nav plugged in. As a result, when I got back in to start the car, my old battery had given up the ghost and was completely dead (soon enough, even the hazard warning lights stopped working).
After being jump started the mechanic put a meter across the battery and said he suspected I may have some issue with the alternator or an earthing wire however, after driving for a while, the battery charged enough to start the car the next morning so the alternator is clearly working to some efficiency.
Whilst driving after the jump start and while the battery was still very low on power, I noticed that when I applied the foot brake heavily, the engine would stall but I managed to bump start it on the existing forward momentum. I wonder whether this occurred because applying the foot brake caused the power draw on the alternator (from the brake lights) to be too much and there was no longer enough power to spark the engine (I am not much of a mechanic, this is only a suspicion).
Normally, I would think the alternator provides more power than the battery and this should not occur but if the alternator wasn't working at maximum efficiency, is this a plausible scenario and how would I confirm?
I have since swapped in a new battery and the stalling has gone away, additionally, although I tried not to apply the brakes too heavily the morning after, I had no stall incidents with the slightly charged battery.