Originally Posted by Chuck_Michigan
Phil's Load/Battery Supply comparison is how you want to think of it. He explained it very well.
I'd mis-read your post to mean that higher capacity batteries were a problem, though also something with alternators.
It's one of the reasons I never let them add the acid to my batteries. The vendor usually wants to add the acid for you, give it a 'quick' charge (14 volts and lots of amps), and then have you out the door as soon as he's done.
I guess I'm lucky, the vendors I know have a few batteries on a proper charger before they sell them. Our "consumer gaurantees act" makes them make sure the batteries are good, otherwise annoying pricks like me will be making damned sure they give us a good new battery for free if the old one only survives a couple of years.
So that super high output alternator is going to be trying to do the same thing to your stock sized battery during it's life every time it enters the charging state.
While some chargers themselves have circuits that'll draw extra current through the battery, I've not seen it in alternators. Most vehicles I've seen the battery is in parallel with the alternator, so I'm struggling to see how it can be made to draw extra current.
I've known a number of motorcyclists to fit stronger alternators to their bikes because the load of extra lighting or other attachments draws more power than the standard one can reasonably handle, but have kept the standard battery (one mate has a car battery in his side car to power his popup caravan, and a LOT of extra electrical stuff needing a full-fat car alternator). No one's had any issues with batteries dying prematurely
That's where I'm trying to understand the claims - the battery is in parallel with the alternator (checked a few diagrams while writing this
), there's nothing that would force the battery to draw extra current, so why would a stronger alternator make the battery charge faster than it wants to?