It's a WFCO 8955PEC, which is a 3 stage converter/charger but it never charges
batteries pass 13.3V. It goes in bulk mode only when batteries get pretty low.
A battery is fully charged at 12.6v, but that is measured at rest. Anything above that is just a surface charge and dissipates within a minute or tow of any load. When you see 13.6, or 14.3 (the alternator output voltage), it merely reflects the most recent charging voltage.
Once your battery reaches its steady state of charge, use a battery hydrometer to measure. I'll bet the specific gravity reading will show you got a 100% charge at the 13.3v rate.
Bulk charge is supposed to happen only when the battery is very low. The battery has internal resistance that prevents higher charge rates when it is partially charged.
This article should help you understand how batteries are charged and why three stage chargers do what they do.
All About Battery Chargers â€“ Battery University
Battery manufacturers typically recommend a charger whose max rate is at least about 15% of the the battery amp hours it works on. For example, if your battery bank has a capacity of 225 AH, then a charger with a max rate of 35 amps is sufficient. A charger with a max of 20% of the AH (45A in this case) is about all that is practical where maximum charge speed is desired. Anything beyond that is usually wasted capacity, since the battery cannot accept more/faster charging anyway.
You started out stating you wanted to add a dedicated
charger. Why is it you think a separate charger will provide any more or faster amps than the WFCO? Using a separate
charger has little, if any advantage. A larger or better quality unit might have some benefits, but the charge algorithm in the WFCO 8955 is decent enough.
I'm just trying to save you money on something that will likely not bring you any benefit at all. If you feel the Xantrex will help, go ahead. It won't hurt anything except your wallet.