Here we go again...
Please, do not confuse alternator out-put with battery capacity.
I run a 70A Bosch alternator on my winter-beemer, that is 980W at 14V. I run it at 14V at summer and 14.8V at winter, which results in 1036W then...
I have a 90A that I will install on my summer-bike. That is 1260W at 14V.
I have tested large alternators to any since battery between 14Ah to 100Ah - the battery gets charged, not cooked. No problem.
I have also tested the opposite situation, the beemer stock alternator of 20A (or so they claim...).
It will charge any battery from xAh to 100Ah - it simply takes more time to do it. However, the original beemer charging system have some flaws that need to be adressed, what ever battery that one is using, to optimize charging.
In my VW buss I'm running a 80Ah startbattery and a 80Ah backup. The alternator is a 120A (1680W at 14V). On the older vans one had a 55A alternator and dual 70Ah batteries.
The out-put of the alternator will only tell how much load one can put on it, not how it charges the battery...
If one want more gadgets consuming electric power, one will have to install a stronger alternator. That, can be a bit tricky though...