It's always worth checking the voltage drop between the negative pole of the battery and the case of the alternator.
A difference of 0.5 of a volt can make the difference between a well charged battery or one always on the brink.
I have found on older cars (8yrs+), there is often a degree of resistance in the earth strap from the engine and consequently the alternator, and also in the strap from the negative pole of the battery to the chassis.
I have corrected this on numerous cars using a 4 or 8 gauge wire from the alternator casing to the battery negative pole.
You have to be careful with this, as should the main earth strap ever fail, then you will draw full starting current through this additional cable, and it may melt !
1989 W124 300E
1991 R129 500SL