2006Audi A4 3.0tdi not starting

Hi

I am new to the forum and have had my 2006 Audi A4 Avant 3.0tdi for around 6 months with no issues.
I have been preparing the vehicle for getting a towbar fitted so bumper and crash bar removal.
While doing this I disconnected the parking sensors (currently in fault) and the Bose speaker unit in the boot.
Moved the car forwards for more room all OK.
Carried on working and went to restart car and the battery had gone nearly flat my own fault.
Now the issue I tried to use jump leads to my wife's countryman and start of but car just turns over and doesn't start.
I can hear the low pressure fuel pump after trying to start seems OK.
Checked relays the are OK.
Battery isn't currently holding a good charge when engine is started it drops to around 9 volts with no jump leads.
Using jump leads I still saw a drop to around 10volts
The car feels like it is being starved of fuel but I have not changed anything or messed with any connections yet.
No codes come up in VCDS

Could this problem of starting all be to do with the battery getting low earlier or do I possibly have another issue? (Battery on trickle charge at moment)

Sorry for the long winded question but have tried searching without any answers.

Thanks, Ross

I would try a new battery as the first step. Is the alternator charging correctly? The brushes wear out.

Hi
Thanks have had battery on trickle charge all night and is measuring as it should.
I ran a full scan on VCDS and came up with a few codes but after they were all cleared. No fault codes were shown.
Should say this only happened after u put bumper back on.
Also forgot to mention airbag light was on due to me disconnecting switch at. Back of glovebox to repair hinge so used VCDS to reset not sure if this has anything to do with it.
So bumper was removed/replaced
crash bar removed/replaced
Rear sensors disconnected/reconnected
Rear sounder for parking sensor in avant boot disconnected
Connections to parking sensor unit disconnected/reconnected (checking connection for ssensor fault)
Airbag light on used VCDS to reset
Now car cranks well everything works no codes showing up but just won't fire
3.0tdi
Been searching a lot with no avail

Now wondering if something to do with airbag light reset
Thanks

Is this forum support? Might be better off reposting in correct section, might get more help then.

Moved to correct section...haven’t done that in a while!