BigEjit

As an example, here’s an 8 hour data logged session from a 2014 2.0TDi VW Caddy with a 096 AGM. It shows fluctuating voltage based on current demands from the vehicle. The ‘A’s in the graph are engine starts where current draw is at its maximum. Depending on the system current requirements, the voltage is changed to allow charging, maintaining or battery only power supply. There is no S/S feature on this vehicle but the energy management principle is the same. Neg current shows when drawing off the battery and voltage is low, Pos charging current when the alternator is operational and voltage is high. There is a significant current draw midpoint from an external device spliced into the harness that didn’t switch off with the ignition. The charge profile immediately called for high current next engine start to recover the battery charge state and tapers off back to normal once the battery is good. its constantly monitored and adjusted.

As a suggestion for regularly carrying super long lengths, how about using roof bars and fabricate a T topped staff off the front towing eye as a support to tame the random flapping aboutery. That’s got to be better than hacking about with the doors open, surely??

Seriously, driving with the back door open on any vehicle is never a good idea. Having done fume ingress testing on vehicles in the past, it doesn’t take long to fill an unpartitioned cabin with carbon monoxide especially on squarer vehicles. Dangerous levels of CO can be present and you won’t even know about it. Opening the front windows for more ventilation creates a vacuum and just draws more air and fumes in from the rear of the vehicle. That’s why the dash warnings for open rear doors never go away when moving. As for the lighting, you are asking for a software change, or you could just overlay manually switched lamps into the load space or even get a usb rechargeable LED head torch for a tenner. They last hours on a single charge and are really good.

Roofbars....... And bunch of lashing straps.

Couldn’t be bothered with the effort. It doesn’t get dirty in there, there is a cap to plug the socket when not in use and you can’t see anything of the opening unless on your hands and knees. And if you do use the cut out as a cover, it’s just more faff to mess with when putting the swan neck back in.

There’s not that much info out there for looking after batteries which is surprising considering every car for the last 90 years or so has one. I guess it’s not that interesting as a subject. BU pages are probably the best available for free. For AGM, the charging should be voltage limited to 14.8v max, current can fluctuate within this limit. Flooded batteries are charge current limited. All batteries need protection from overcharging so they don’t dry out. AGM naturally hold less electrolyte over wet flooded batteries and need more protection from this but certain duty cycles will force a loss of moisture from the assembly regardless of tech. Pressure valves in the lids aim to stop this water loss (Valve Regulated Lead Acid - VRLA) and in-vehicle charging strategies hold the battery in a confined charging window to protect it from overcharge and try to recover it from undercharging depending on available engine run time. Excess heat is also a silent battery killer from overcharging and environment and is bad for all lead acid batteries. Too much heat and the lead plates decay and turn to mush, it takes a while for this to have a noticeable effect but once started, it’s not reversible. Equatorial markets go through batteries quicker than temperate climate markets. It’s also the reason for the module on the neg post has temperature sensor so that charging is restricted relative to battery temp. General mis-information leads folks to think cold weather kills batteries. It doesn’t! It shows up weak batteries damaged from summer heat/discharge/overcharge. The insulation bag the battery is covered in is to reduce the speed of heat soak from the engine bay when stationary or slow moving with no airflow underbonnet. Regulations only allow AGM to be fitted inside a vehicle cabin for occupant protection from spraying acid in a crash situation. It usually ends up in the load space somewhere accessible but then needs to be bigger to overcome the losses in heavy high performance cabling stretching the length of the chassis adding more weight. Then you get those folks pulling the fly lead off the battery module to inhibit S/S and throw all these carefully engineered compensation factors out the window! 🤦‍♂️ Dried out batteries go pop!

That is a result if the charging strategies set up in the software and after this year, a dramatic shift in how vehicles are used. The batteries themselves from the top manufacturers are the best available but they are built to incredibly tight specifications and tested to more stringent durability requirements. OEM’s also have to remove the use of hazardous materials and get weight out of the vehicles as much as possible to achieve emissions targets. This just puts more pressure on getting efficient use out of the smallest batteries they can fit, as much as possible. The batteries will last if they are looked after from the moment they are first fitted. They have to be protected from discharging and critically when they are in the dealer network from new