JP

I'm sure it did JK, but, for clarification, it was only charged in the course of driving. I haven't had it on a charger.

Out for a short spin today ~30 mins. No idle problems at all. Here are some further voltage readings for comparison after this morning's drive: Everything off, FIA off: 12.84V Everything off, FIA on: 12.84V Lights on for 10s, then switch off: 12.72V Cranking: No initial momentary large drop visible on my multimeter. Initial cranking at 10.90V, which dropped smoothly while cranking to a steady 10.71V. And looking at the revs drop as per @revilla posting above, I think I see a momentary pause during the fall: Videopro 20240427 110103-1.mp4 So, I now have a new IACV sitting in a box. I guess I might as well fit it...

If anyone only wants 4 of these, I would be happy to take the 5th - I'm after a spare.

I'll recheck it after driving, but I don't think I should have to put a new battery on a charger...

Battery and IACV arrived today. Battery fitted, but not test driven yet. However, I thought I would test the voltages on a fresh battery straight out of the box from Tayna. Here are the numbers for comparison: Voltages: Everything off, FIA off: 12.54V Everything off, FIA on: 12.54V Lights on for 10s, then switch off: 12.40V Cranking: No initial momentary large drop visible on my multimeter. Cranked steadily at 10.35V. Engine started (on the button, no throttle needed), idling at 13.95V. No 3000rpm voltage tested this time. Current IACV could be felt "stepping" briefly after switch off. I'll drive the car over the weekend. If it fails at idle again, I'll change the IACV. If I get to Sunday and it hasn't failed, I might change the IACV anyway, because the new one is shiny and new...

Will do! Battery first and I'll keep the IACV in the boot just in case...

Right! I've lost patience and ordered a new Banner and a new IACV! One of those must fix the problem! Having thought about this more, I do recall the cutting out happening once before, before I took the car off the road in about 2008/2009. It ran fine again afterwards, but perhaps that is a sign of a failing IACV... I'll look at lighter batteries next time once everything else is sorted. Thanks for all the help and guidance!

@BigCol may I ask why? Was it only weight saving? The Banner seems to have greater capacity and cranking then the others. For me reliability is my primary concern as mine is mainly a road car with occasional track days.

Or £40.66 / kg if I should be looking at this one: https://www.tayna.co.uk/motorcycle-batteries/odyssey/pc680/

£27.18 / kg! (inc VAT) https://www.tayna.co.uk/car-batteries/banner/53034/ vs: https://www.tayna.co.uk/motorcycle-batteries/odyssey/pc535/ If I've selected the correct Odyssey....if I haven't, it could be a lot more!

Thanks again all. I've just caught up. Been through the Best Battery thread again and (other than the sealed / unsealed point) I'm struggling to find a reason not to stick with the regular Banner at ~£80.

I believe Chris is managing it by himself. Bear with him - he is incredibly helpful and knowledgable and I am sure he will help as soon as he is able to do so. In my own experience, sometimes he responds immediately, sometimes it takes a little longer - if it has been a few days, there's no harm in giving him a gentle nudge.

Wow, my primaries are from Powerspeed c.2002 and seem fine and that's after 14 years of no use being stored in a draughty barn...but with no wrap...

@revilla - thank you. I will replace - looks like a decision between a Banner and a Powervamp PC535. I understand that AGM batteries require a different charging profile from standard acid. Is that an issue on a 7 or is it only an issue for cars with an ECU that manages the charging pattern? I replaced my LA battery with an AGM one in my Boxster and was advised that I should have stuck to regular LA as the charging would not be properly suited. As for the cutting out and failing to start and stay started on the starter button without throttle, it does seem to have resolved after removing and firmly reseating the HT leads. Would it make sense for that to be an explanation? I'll listen again to the IACV and make a note of when I hear it...

@Jonathan Kay - Following charging the battery overnight, I now have these numbers: Voltages - tested on a cold engine as soon as charged battery re-installed. No driving between charging and testing: Everything off, FIA off: 13.24V Everything off, FIA on: 13.23V Lights on for 10s, then switch off: 12.68 Cranking: initial momentary drop again to around 7V, but too brief to be sure. Settled cranking at around 9.60V while cranking for a few seconds. (Cranking with king HT lead unplugged from distributor.) When stopping cranking I noticed, what I guess, is a stepper motor sound from the IACV, so I guess that is working - or at least doing something. I didn't recheck voltages at 3000rpm as it was a little early in the morning for my neighbours! From the figures above, I guess I need a new battery? I'll trawl the thread above again, but I suspect a std banner will be in order...