What should voltage read out be on MFD when not running - Page 1 - Boxster/Cayman - PistonHeads UK

Is the voltage read out on the MFD accurate? And what should the voltage read out be on the MFD when ignition on but engine not started? My voltage sits bang in the middle of the line, its around 11.8-12 volts. I have it hooked up to a CTEK but only once a week until it gets to the float step.

Depends on what battery you have fitted...

In my case it's a Banner, part number 999.611.080.12, 12V 80 Ah 800A

There you go:

Thank you

Mine was dipping down into 11.7-11.8 territory (original battery on a 60k mile 2018) so changed it towards the end of last year. I park on the street so trickle charging isn't really an option and didn't want to risk it, sometimes batteries seem ok then suddenly they're not. On a brand new battery of equivalent spec to the OEM one, it's about 12.2 before starting now. Looking at the battery voltage causes me way more stress than is normal, worrying about the energy management is working ok 😂 i'm just going to start leaving it on tyre pressure display.

11.8V to 12V sounds shagged. My battery is 12.3V -12-5V After standing for 2 weeks AGM battery state of charge table. Edited by elan362 on Saturday 10th February 22:04 Edited by elan362 on Saturday 10th February 22:05

For the MFD to show voltage you've unlocked the car and turned the ignition on. This already puts a load on the battery (fuel pump, ECU, internal lights etc) and that drops the displayed voltage by 0.2-0.4V. If you want the true resting voltage then fit a battery monitor or before opening a door/frunk measure the voltage directly. In short, the MFD is correct and a normal reading will be in the range 12.0-12.4V. If doing short journeys then use Sport mode, it charges at a much higher rate rhan Normal/Eco.

SV_WDC said: Is the voltage read out on the MFD accurate? And what should the voltage read out be on the MFD when ignition on but engine not started? My voltage sits bang in the middle of the line, its around 11.8-12 volts. I have it hooked up to a CTEK but only once a week until it gets to the float step. Brilliant, I’ve come on here to ask exactly the same question, word for word. I’ve dug out an old CTEK (OPC supplied) as I not driving my GT4 right now, but wondered if it’s not working correctly; sounds like it’s OK then.

M11rph said: For the MFD to show voltage you've unlocked the car and turned the ignition on. This already puts a load on the battery (fuel pump, ECU, internal lights etc) and that drops the displayed voltage by 0.2-0.4V. If you want the true resting voltage then fit a battery monitor or before opening a door/frunk measure the voltage directly. In short, the MFD is correct and a normal reading will be in the range 12.0-12.4V. True. I've got a Bluetooth Victron Smartbatterysense (SBS) https://www.victronenergy.com/meters-and-sensors/s... fitted, so I can keep an eye on the battery voltage without having to unlock the car and put load on the battery

M11rph said: For the MFD to show voltage you've unlocked the car and turned the ignition on. This already puts a load on the battery (fuel pump, ECU, internal lights etc) and that drops the displayed voltage by 0.2-0.4V. If you want the true resting voltage then fit a battery monitor or before opening a door/frunk measure the voltage directly. In short, the MFD is correct and a normal reading will be in the range 12.0-12.4V. If doing short journeys then use Sport mode, it charges at a much higher rate rhan Normal/Eco. Thanks, where's the info on Sport mode recharge rate? I'd had thought it reserves more for the car in that mode (as on GTS/GT cars it activates other things like the third radiator).

SV_WDC said: Thanks, where's the info on Sport mode recharge rate? I'd had thought it reserves more for the car in that mode (as on GTS/GT cars it activates other things like the third radiator). It's not in the Manual. However, if you have the Voltage displayed on the MFD then selecting Sport whilst driving bumps the value up approximately 2v from that in Normal. The alternator has an upper limit of 15.1v and I have seen this on a battery which was probably at 60% capacity. The thinking behind the lower charge rate in Normal is to minimise load on the alternator and hence engine. Normal does everything possible to improve fuel economy/reduce CO2 figures and this is one part of that. It won't limit performance. Most vehicles these days will reduce ancillary loads on the engine when the pedal is on the stops.