Thanks for the views, i am from the uk, the chargers are standby chargers (or float chargers). They remain at 13.8v regardless of load, obviously up to their stated capacity.
I spoke to the HSE (health and safety executive) and they basically said that if i am competent in my repairs and show correct health and safety procedures, and record all repair details i will remain on the good side of things!
I am waiting for more clarity from the Trading Standards people in the uk, as they would be the group 'chasing' me if things went wrong.
Liability insurance is a must i feel.
As regard the testing, i perform output tests, volts vs amps during various stages of load, i intend to start recording this detail.
Does it really need a PATS tests as its not considered a Portable piece of equipment?
The earth leakage would be tested by my connection to the mains socket i have which has a residual current device (RCD) built in, if only at fault stage...at least it shows no earth leakage.
I suppose the only thing i am not testing is the insulation resistance, apart from the obvious visual checks and ohm meter checks.
Any way i'll keep you informed as to the 'official' outcome when trading standards call me! wish me luck.