charge.

[claud]

i have a bugging alternator problem .now ive tested the charge as putting out 13.5 v at the b+ connector with high beams on. my pulley is too big im told keeps revs too low so wont kick in to charge unless revs are over 1500. thats ok long as i dont sit at idle too long and switch off then restart.
now new big 11 plate bosch battry still hasnt been fully charged up? it reads ok i have a volt guage set up desides the battery in the engine bay to keep a close eye on the thing.new inbuit reg.
it still keeps losing charge. ive disconnected all accessories radio lights,fans plug ins. to cancel out volt/current drain. the only thing still on is the immobilisor from wa. std rego unit.its a cut out that has a blinking light.surely this cant be the problem cause it never has been till now.
a quick trip to a electrician told me to place a fuseable link wire 6mm to the batt from b+ on alt.? why should this work or be necessary if there never was one here before? doesnt this bypass the diodes main job of overcharging the battery?will this stuff my battery?