Limiting current to Aux battery?

RoyB wrote:
Battery science says if you hit a depleted wet cell deep cycle battery with 14.4VDC it will only demand 17-20AMPS of DC charge current and it will bring this up to its 90% charge state in a three hour period.

I am not sure that's an accurate statement. That might be true with some small battery that you can fit in your hand, but not with something larger. I am talking about a dual purpose standard marine battery you can find at Wal-Mart. They are used for trolling motors on boats and starting boat engines. They can crank over an engine, so they can supply 600A. If they can supply 600A, then they can accept it too. You cant really design a battery that can supply a large amount of current without also being able to accept the same amount. In other words, if a particular load were to drop a fully charged battery from 12.8v to 11.8v under load and that amounted to 100A of current to support that load, then charging the same battery discharged to 11.8v at a voltage of 12.8v would also require 100A (briefly anyway).

Fast forward to real world, my battery can provide 650 marine cranking amps and 80AH @ 1A for 80 hours. The standard for marine cranking amps is the max load the battery can support for 30 seconds and maintain a voltage of at least 7.2v. So if the battery can supply 650A for 30 seconds before falling to 7.2v, that would also mean that if the battery were discharged to 7.2v, it would take 650 amps for the voltage to rise to 12.8-12.9v over the course of 30 seconds.

I know that 7.2v is beyond what anyone should discharge a battery to, but it illustrates my point that the battery can both discharge and charge at a rate of far faster than 20 amps, and I am trying to prevent that from happening.