Audi A4 Avant 3.0l Quattro B6 won't start on key but will jump start

[Finder]

So basically the battery was dying due to a faulty boot lock, car would start on the key if it had a good run otherwise I had to jump start.  Managed to replace the bootlock and get the car into my garage to charge and now battery is ok - green light on Yuasa battery and it is getting charged by alternator and also CTEK charger says it's ok but it won't start on the key - it will do a single slow turnover at best and then click nothing but it still starts from a powerpack first time.  I've been told this is probably a bad ground and/or the starter solenoid question is where do I check for bad ground and is it possible to just replace the starter solenoid or will it need a whole starter unit? I believe to get at the starter I have to take the front right wheel off?

Any help appreciated

[Magnet]

Hello David, 

I’m not quite following your logic as to why you are suspecting earth leads, starter motor - or solenoid, when you say the car starts well on a jump start. 

The symptoms you describe are classic sub-standard battery issues, so please do not concern yourself about anything else until you  have confirmed the battery is serviceable - which I doubt it is. 

If this were mine, I would be fully charging the battery overnight, and if it starts, drive it around to your local Halfords and have the battery tested. If the battery needs renewing, would I buy one from Halfords? The answer lies in looking on eBay for the correct battery for your model from retailers such as Battery Megastore, Tayna etc. and compare prices. Personally, I only buy 4 or 5 year guarantee batteries by Varta/Bosch - you may find others cheaper, but....

Perhaps you could let us know how you get on.

Kind regards,

Gareth.