I noticed in another members profile signature that he has a DLS-55, WIbadger. I would guess he could weigh in with some facts on how well the charger works.
Yes, I installed an IOTA DLS-55 with internal IQ4 (purchased thru bestconverter.com). As described by Crabber50, the DLS-55 comes in a couple of different flavors.
The first choice is whether you want a unit that has an external dual voltage jack vs a unit without such a jack. If you opt for the external dual voltage jack unit (IOTA lists this as "DLS-55 (55-amp power converter)"), it comes included with a dual voltage plug (don't confuse this with the external IQ4 plug; they are two different types of plugs). If you don't use the included plug, the unit is a two-stage charger that puts out a max of 13.6V. If you use the included plug, the unit is a two-stage charger that puts out a max of 14.2V, which can be convenient for occasional fast charging. As an extra accessory, you can purchase an external IQ4 plug, which plugs into the same external dual voltage plug. If the external IQ4 plug is employed, the unit becomes a three-stage smart charger, which provides longer and safer use of your batteries.
The second choice is to opt for a unit that has the internal IQ4 (ie, a three-stage smart charger built into the unit) (IOTA lists this as "DLS-55 (55-amp power converter w/IQ4)"). On my unit, there are no external voltage jacks, but if these units have one, the jack will be disabled.
As to which unit to purchase, it all depends upon your anticipated use/needs. A person such as Crabber50 finds it useful to have the ability to switch between a two-stage charger (13.6V or 14.2V) and a three-stage charger (with the external IQ4). I, on the other hand, didn't care for a two-stage charger option, so I opted for the built-in IQ4. (IMHO, it's better to employ a three-stage charger for RV use since it does a better job of properly re-charging batteries). Alternatively, if your TT currently has an IOTA converter w/external dual voltage jack, the purchase of the external IQ4 plug will suffice.
Another issue to consider regarding the IQ4 external vs internal choice is whether you want the ability to monitor the LED indicator light (the LED blinks to indicate which charge mode the DLS unit is currently in (Boost, Absorption, or Float.)). For units with the internal IQ4, the LED indicator lights are affixed to one side of the unit. Depending upon the location of the converter and its mounting orientation, visible access to the LED lights may be obstructed. The external option allows you to monitor the LED indicator light away from the unit. Although seeing the LED status is “cool,” the best solution if you want to do remote monitoring is with a volt meter. Seeing the voltage is more informative than simply seeing if the LED is blinking or not. (I monitor my voltage via a Trimetric battery monitor).
IOTA provides the following specs for units with the IQ4 (external or internal) for 12V battery voltage:
14.8V = Bulk (2.46 VPC)
14.2V = Absorption (2.36 VPC)
13.6V = Float (2.26 VPC)
12.8V = Low trigger
14.6V = High trigger
15.2V = Over voltage fault.
I won’t start a flame as to whether the IOTA is better than the Progressive or vice versa. Do a search on rvnet and elsewhere for various opinions. Whichever way you go, know the specifications of your batteries and match with the converter specifications. It is not true to state that
14.8 volts is what is needed to fully charge a 12-volt battery.
It all depends upon the specific battery specifications.
For example, I have Interstate GC2-XHD golf cart batteries and the Interstate charging recommendations for these batteries are:
Bulk @ 14.46 (2.41 VPC);
Absorption @ 15.3 (2.55 VPC); and
Float @ 13.4 (2.23 VPC).
Compare these recommended charging specs to those of the IOTA.
Regardless of which converter you choose, your batteries will never see anything above 13V if (a) you have a relatively long circuit and (b) you don’t change the 8AWG wiring that is normally used. The problem: voltage drop. If you don’t address this issue, you won’t be taking advantage of the charging capabilities for these smart chargers. I swapped out the 8AWG for 4AWG, resulting in less than a 2% voltage drop.
Finally, after three years of use, I have had no problems with my DLS-55. It (quickly) re-charges my batteries to 100% state of charge based upon the reading from the Trimetric monitor.