My GTI Keeps Playing Dead

[LC5F]

Bit of a gremlin in the Gti, hoping its something obvious-

3-4 weeks ago, first drive that day, unlocked the Golf with the fob, welcome lights popped on as normal, jumped in and turned the key - nothing, no dash lights, just a very slow starter turning the engine, this turned into your standard low battery clicking after only a few seconds.
Got out looked around, tried re-locking, it worked and then unlocked with the fob, jumped in again and it started as though nothing was wrong...!

Last Sunday, a short journey to the shops, returned to the car, fob unlock, jump in turned key, this time nothing - no lights no starter, hopped out shut the door locked + unlocked and it started up again.

This morning, going to work, came outside pressed the fob and nothing, no welcome lights, no central locking noises. Didn't have time to look at it, assumed battery fully flat, had a bit of time before Uber showed up so decided to pull the battery to charge it up, to my annoyance detaching the earth set the alarm off! The Golf seemed to come back to life! already committed to the Uber, so continued removing the battery - I noticed the indicator was Green when I put it on charge.

Tonight, Battery fully charged & back in the car, all good it seems.

What could this be acting up on my 2006 BWA DSG GTi?
Suspects:
Battery - I  replaced this 3 months ago, its a Yuasa Silver 5000 80Ah 760A - I know they are not the best, but had a nice discount with Halfords trade card
Head unit - I replaced the standard RDS300 unit with an Xtrons Android unit, its VAG specific - built to fit the dash and works with canbus, first couple of weeks it was a bit crashy, but there has been no problems last couple of months.
Bluetooth ODBII reader - for Torque app, this reports 14.3 volts charging, this tends to be left plugged in
Welcome Home lights - got Xenons, I dont think this is helping.
Heated seats - been running on level 2

Am I asking too much from the Golf charging system?
or is there something failing?
Does the Canbus Gateway need upgrading?

[Octoparrot]

First I'd try unplugging the obd reader and see if it helps, if not I'd next look at the canbus.

[bobby_fodge]

If if was the battery I'd expect slower starter motor initially and then not even that after a few more attempts to get it to start. That's what i've seen with batteries low on charge.

Could it be that you had the stereo, auto lights and AC on for that initial attempt to start, which may be have been too much for the battery to start the car with. You then switched off some of those and then the second attempt was successful?

I have a tiny Odyssey battery which doesn't like it when I try and start the car with loads on electrical items on. 

I took my aftermarket headunit out as it was draining the battery overnight. Only started doing that after being fine for 18 months.

[LC5F]

Thanks for the replies

I don’t recall switching anything off in the first 2 events, it’s more like the golf had no battery - but the fob had just unlocked the door.
No sign of flat battery when it started working, no slow starter.

Well, I’m going to keep everything switched off and keep a 10mm spanner in the car in case I need to reset the battery

[bobby_fodge]

I keep one of these in my glovebox, it really does work.

https://www.amazon.co.uk/EC-Technology-Portable-22400mAh-Smartphone-Black-Red/dp/B00F5Q4F0U/ref=sr_1_22?crid=1RUKDBYN3GJA1&keywords=car+battery+charger+usb&qid=1578517243&sprefix=usb+car+charger+batter%2Caps%2C210&sr=8-22

[LC5F]

Thanks Bobby - each time the battery was not flat, just the golf playing dead

[GVK]

Check your earth strap from gearbox to chassis.

[bobby_fodge]

You scanned it with VDCS when it's playing dead?

[LC5F]

Well, it’s been behaving itself over the last 2 days - I haven’t had the Bluetooth old plugged in, and before switching off the engine I turn off auto lights and the radio. Not used the heated seats at all.

@gvk - will have a look at my gearbox earth point at the weekend, need an excuse to change my inline thermostat

@bobby - not done any scans, suspect if I did catch it in the dead state it wouldn’t scan. I haven’t got a VCDS kit that works with Mk5 - I do have a icarsoft vars 2.0, will give that a go at the weekend too.

[LC5F]

Weather wasn't the best, but managed to get some bits and bobs done.

looked at the inline thermostat - defeated by the spring clips being inaccessible, decades of VAG ownership - this is a first for me!

Gearbox earth strap - easy to access, removed it all clean at contact areas, as it was out a quick wire brush and spray of contact cleaner and its back on the Golf.
 
Did a full scan -
EVAP error 001089 will look into the N80 next chance, Apart from that nothing jumped out apart from live voltage was under 12v - should be 12.6v?

Scanned the Gateway i have a 1K0907530F, I understand it was only from revision L that the parasitic drain was fixed - suspect this may be my problem. Will keep switching the head off before the engine.

[titchy]

check below fuse box there are a few bolted connections I had green corrosion between a live and earth causing drain wire brushed solved