Several years ago, I went from lead acid batteries to AGM's. Since then I've read that if you make this conversion you have to change the charging systems - both the alternator and the charger/inverter. Would those who are knowledgable on this please explain, including what exactly I have to change. Thanks.
If you have an I/C or inverter charger it should be fine an may just need you to program if for the manufacturers suggested absorption and float voltages. If it has the option for temperature compensation AGM's can certainly benefit from this.
If you actually want to take advantage of AGM's benefit of higher acceptance rates, eg: faster charging, then the stock alternator simply won't cut it and is woefully under-qualified..
Also some stock alternators have no internal temp compensation and many an alternator has been cooked by AGM's demanding full output for hours on end. A heavy duty alternator, specifically designed for long term high output use, will compliment your AGM's but is not always "necessary".
To my way of thinking spending the huge dough on banks that are arguably shorter lived than flooded deep cycle and then not taking advantage of their benefits, such as fast re-charge times, is an odd way, finances wise, to buy batteries. Perhaps you bought them and they are mounted on their sides and in this case they are worth it.
Lifeline wants to see an alternator of no less than 20% of the banks capacity at the 20 hour rate. Enersys/Odyssey/Die Hard Marine AGM's want to see an alt with a minimum output of 40% of capacity. These are minimum suggestions to get the best life...