The bosch alts are usually very reliable, but can/do suffer from heat damage sometimes due to nearby "cooker" unit, fried the cables on my alt, after I made a engine mount heater shield.
Just stick metre on, just did a alt swap on me dads 4i on friday, he only nicke dme spare cossie one, direct fit on his v8 lump in his car, his alt was working fine till he booked it in for the mot, then decided to pack up, and have a hissy fit with 3 bad connections at the same time, he's still got my 3 door hubs from 5 years ago I loaned him!!
As said there is normally enough residual magnetism to start the charge cycle if warning light bulb blows, by revving to around 3-4K.
tabetha