Some K revision gateways will give you battery drain.
However i have a K revision gateway and do not have battery drain. Im running 276X firmware in my vRS with the K gateway and that is fine. I've left the car for nearly a month while on honeymoon and it started first time on my return.
There is however a 276X firmware that has the VUCI file from the 110X firmware. This firmware, for 99.9% of people, stops battery drain no matter the revision of gateway. I do know of a couple of people that it hasn't worked for. But the majority it does.
The latest firmware is 276X. If you are not bothered about Voice Control then there is a later 130X (don't worry about no's) but you don't get voice control with this firmware. You also require bluetooth for Voice Control.
If you get a Skoda Rev B or VW Rev C RNS-510 then there is a leaked factory beta firmware (380X) that is currently the most up to date. However to get the features over 276X you need V7 maps.
Just so you understand No's the firmwares go in the following order (X is replaced by a no. depending on unit it goes on. So for example 2760 is VW & 2764 is Skoda) However all the Firmwares for all makes of RNS510 are on the same disc. The unit just recognises it and installs the correct firmware for that unit.
100X (Original for A Rev Units)
102X (Rev A Units)
090X (Rev A & B Units)
110X (Rev A & B Units)
116X (Rev A & B Units)
120X (Rev A & B Units)
266X (Rev A, B Units & Beta for Rev C)
268X (Rev A, B & C Units)
272X (Rev B & C Units, Support dropped for Rev Units)
276X (Rev B & C Units)
130X (Rev B & C Units Voice control removed)
380X (VW Rev C & Skoda Rev B only)
There is Modified 272X & 276X firmware for A units (I am using 276X modified on both of my Rev A Units) which enables you to have the latest on A units.
You can Plug & Play the unit with no coding. However if you have highline it won't show the Nav Instructions until properly coded. But it will still work as intended but on the screen only. If you get Bluetooth that will need to be coded.
Again with the phone not showing in the Highline. Some K gateways will some wont. As Danish has said get the latest CAN Gateway you can get your hands on. They go for around £85 off eBay or about £130 from a dealer (expect more when the 20% VAT kicks in).
My advice would be get a C Rev LED RNS510 and fit that. Fit either the OEM Bluetooth or the Fiscon Basic Plus. I have the Fiscon Basic Plus and am very happy with it. Benefits over the OEM BT is that you can do AD2P bluetooth streaming. There is a newer version of the OEM BT that does this but i'm not sure on the compatibility with what cars etc at the moment.
If you want Firmware i can provide or point you in the right direction (VWNavi.com) where you can get it from.
Maps can't legally be downloaded. However there are ways of obtaining them if you know where to look/who to ask.
I'm Kent if your nearby and can do all the coding etc. Im also in Wiltshire Mon-Thurs (but not from Dec 10 - Jan 3).
Any other Q's just ask away
HTH
Carl