Being such a smart bloke I managed to leave the PWR switch on for the past 5 days after we got home from a trip and flattened my main battery
I remember flicking that switch on to keep my fridge alive until I got it unloaded on the day we got home. Seems that I forgot to turn it off again afterwards. With the exception of one short trip my vehicle has been sitting for 5 days with the Wolfbox mirror, a UHF radio, a Cel-Fi R32 cellular booster and a Zetifi powered smart antenna powered up.
Fast forward to today I got in it and it cranked slowly. It still started without issue (diesel). After start I had the red battery alarm in the telltale panel and a battery volts low message on the infotainment screen. On the Offroad > Electrical screen the battery SOC was 4% and the charging rate was 118 Amps! I then drove 20 minutes to an appointment. In that time the charge rate varied between roughly 40 amps and 100+ amps. The only noticeable anomaly was the HVAC fan was cutting in and out despite it being on setting 2 (a 30 degree C day here). By the time I reached my destination the battery SOC was up to 48%. I checked I had my lithium starter onboard as a precaution then turned off the vehicle. 30 minutes later when I returned the vehicle started normally with no indications of a flat battery.
20 minutes later I was home with an SOC of 100%. I'll do a cold battery load and capacity test tomorrow to check the battery status.
I have the Auxiliary battery option. Clearly the Smartpass has functioned as advertised to boost the flat main battery for the initial start. The ECU then ramped up the alternator to recharge the battery at best rate. Even at idle it was still pumping in over 40 amps. I went from 4% SOC to 100% SOC within 45 minutes of engine operation.
My point? This is exactly how the factory auxiliary battery system is supposed to operate. I didn't plan on doing a live test of a flat main battery but I can tick that off now. If I had a bunch of extra consumers hanging off that auxiliary battery there is a good chance it would not have had sufficient remaining charge to boost the main battery and give me an engine start.
I know the factory setup is unconventional and some owners have ripped it out in favour of a conventional starter and house battery configuration. My dumbass experience today is the scenario that Ineos designed the main and auxiliary battery setup for. And it worked. Of course a lithium starter would also be a backup to a flat starter battery, but there is that note in the owner's manuals about not using a quick charger - whatever that is
