Like they say.
You indicate that it seems to be seeing 14V (ish) at the battery while running, yet it's discharging. If the battery is good (from what you say that's most likely), then it clearly isn't getting 14V otherwise it wouldn't go flat.
The SV Reg/rec is renowned for failing, from what you describe it'd be where I'd look first.
Electrex has been suggested on here before as decent equipment.
http://www.electrexworld.co.uk