Ahhh refreshing to find someone not afraid to turn a dial and not toe the 'plug and play' line.
Heck, the Cheapowatt @ 24$ could meet the OP's desires of a set voltage to hold a fully charged set of Lifeline AGM's at 13.2v, as long as the 'hotel' loads do not exceed 30 amps or so and it is not hooked up when the Lifelines are depleted, as it has no overload protections built in.
http://www.amazon.com/eTopxizu-Regulated-Switching-Supply-Silver/dp/B007KG0ZYIThe PD9245 I recently attached to a lifeline gpl-31XT was a bit strange.
14.56v, 13.73v, and 13.34v were the 'stages', and I never notice it drop to 13.34v on its own. I always forced it via the pendant. I never experimented enough to determine what initial voltage or amp flow caused it to choose 13.73 or 14.56 when first plugged in.
What I find weird about choosing a 13.2v float Via my Meanwell RSP-500-15 on my Northstar AGM(resting fully charged OCV of 13.06v), is that it actually seems to allow the battery to discharge at 13.2v when loads are still present. Often when I chose 13.2v, my battery monitor indicates 13.2v and -0.4 amps, and if I keep it at 13.2v for several hours, then I can bump it to 14.5v and the amps flowing indicate the battery was actually discharging when held at 13.2v.
But, If I bump the MW up to 13.6v float, then the ammeter never reads negative, and if I goose it to 14.5v, amps quickly taper to less than 0.4a indicating the battery is still fully charged.
13.2v float while powering loads and a goosing to 14.5v, the amps will rise to ~ 12, and taper quickly to ~1.5, and then slowly taper after that, indicating the battery was being discharged when floated at 13.2v.
So it appears to me, floating AGM's while unhooked to any load is significantly different than floating when loads are still present on the DC system, and a fine tuning of float voltage when load floating is necessary to keep the battery from discharging a few percent.
I know this goes against theory, but my observations of this behavior has happened way more than once. This was not an issue with my flooded battery. I believe it is because the AGM, when fully charged, requires such small currents to be held at higher voltages, and the flooded batteries require significantly more current to be held at float voltages.
I've tried to find the lowest float voltage I could on my AGM where a temporary goosing it to 14.5v did not see a major amperage acceptance. I can't go lower than 13.5v or the 14.5v goosing reveals some of that top charge has sloshed off the side of the bucket.
So an ammeter and the ability to choose output voltages and observing amperage acceptance at both float and absorption voltages, has been very revealing, and flies in the face of lots of common knowledge espoused time and again on this forum, by some.