I like my Xantrex charger because it stays in the higher 14.4 vdc range longer than the onboard converter will. And even that voltage is lower than recommended for bulk charging by Trojan. For the T-105 batteries, Trojan recommends a 14.8 VDC bulk charge voltage (and 13.5 float / 16.2 equalize). The onboard converter never even gets close to the recommended equalize voltage, which is hard on batteries.
It's required that flooded cell batteries bubble and outgas oxygen and hydrogen while charging, because that provides a means to desulfate the lead plates, plus it mixes up the electrolyte so that it doesn't stratify (concentrated electolyte at the bottom of the battery, and a weaker solution at the top).
When charging batteries are bubbling off gasses, that's a good thing - as long as the recommended charging voltage isn't exceeded, and water levels are topped off regularly. Because my onboard charging system never reaches the recommended charging voltage, I firmly believe my T-105 battery's lifespans have been compromised, and their performance has suffered over time. In other words, I believe the onboard charger is inadequate and damages the batteries.
Check out the specification sheet for Trojan T-105 batteries: