As mentioned in other reviews, this charger has active power-factor correction (PFC), very important for getting more usable power out of small generators! It's strange they don't advertise this feature, which let me pull 35-40% more charging power from a little Honda EU-1000i, vs. the similarly efficient but non-PFC Iota DLS-27-25 this unit replaced, which had to be derated from 25A to ~22A out to avoid overloading the Honda. It's nice having a simple adjustment dial for limiting current; my Iota required physically changing shunt resistors inside.Adjusted for about 74% of max output, this AIMS delivers 740W (28.0A @ 26.4VDC) into my 24V battery bank while pulling 890W (900VA) AC from the generator, at an excellent 0.97-0.98 power factor as measured by a Kill-a-Watt. 740W out / 890W in = 83% efficiency, as specified - good but not great. It uses ordinary Schottky diodes on the output rather than synchronous rectification, which could have boosted the efficiency a bit.The main negative I see is that it draws a small but significant parasitic DC current, if left connected to a battery bank with no AC power source - this is worse if you leave its toggle switch on, a full 5.0W (0.2A @ 26V) on a 24V bank, or 3.2W at 12V (0.24A @ 13.4V), but even with the switch off it pulls a constant 0.11-0.13A depending on DC battery voltage (about 1.5W at ~12V, 3.2W at ~24V). This is as much as leaving a small 12V incandescent bulb running constantly, or several LED bulbs, and could easily drain a battery if left connected for a long time with no power, as might happen on an RV or boat. So, if you plan to leave this permanently wired to the batteries, I'd recommend a suitably rated DC breaker, switch, or relay to isolate its output when not actively charging.In my case I already had a 50A DC breaker in series with the output, and with a manually-started generator it's hardly any trouble to make sure that's breaker's turned on only when charging. An auto-start generator might require more attention.As soon as DC voltage is connected to the terminals, a relay "clunk" can be heard inside-- I suspect it's the large 100A relay (CAR1AP100DC12-S) showing in one of my photos, perhaps meant to protect against reverse polarity (coil wired to DC terminals w/diode in series?), or else something to do with the automatic 12V/24V detection and switching. If so, its coil current may account for most of the ~120mA constantly drawn even with the power switch turned off. Parts of the control circuitry appear to be powered from the attached battery as well.If you connect AC with no battery attached, though, it doesn't power up at all, pulling 0W AC (but 11-20VA; probably filter caps across the line) and putting no voltage at all on its DC terminals. This means you can't charge a completely dead battery, and someone not expecting this behavior (which the manual fails to mention) might think the charger is completely dead.The manual could use improvement generally, and is completely wrong in some places, like where it mentions 12V-vs-24V having to be manually selected.Other than that, the charger seems to be well-built, with good input filtering and noise suppression. I've attached some photos of the internals, taken when I briefly opened it to reverse the fan airflow direction to avoid fighting natural convection when mounting it when the DC terminals facing up. It's easy to get into, with only 6 small screws to remove and no seals, adhesive, etc. The large electrolytic caps are "YST" brand, which I'm not familiar with. I can't read the brand markings on the three smaller ones behind the fan without disassembling further.There is at least one trim pot on the control board (fixed in place with some glue or epoxy material), which might be usable for fine-tuning voltage if none of the four DIP-switch selectable defaults quite fit your need, though I didn't try this. Without opening it up, it may also be possible to dial down the voltage by plugging a variable resistor into the battery-temp sensor jack.I have been designing an appropriately-sized PV array and recently got a good hybrid charge controller. At some point, I actually stopped as I realized, the panels cannot be recycled. I chose to go with my old favorite, a good sized generator. I looked at various power modules and compared (by eye and review) the different options. DC-DC choppers, various charger types and then I found this one. I was sold on the PFC which is a HUGE deal. I grabbed one.I have not had this very long but the load testing has been outstanding. It is able to keep up with continuous, pulsed power devices (such as monitors, UPS's and regular inductive loads. I wish it had synchronous rectification as there is a requirement that there will be an off draw unless it is disconnected from the battery load. Schottky diodes are employed and that is the only downside here. Otherwise, once I have the new generator in place I will test that next. The unit appears to be very sturdy and as a bonus, the input VAC can be 70-140 VAC with auto throttling (!!) of the output current instead of shutdown for line voltage! It is even somewhat tolerant to variable AC line frequency (I don't yet know about how it deals with line harmonics coming to the output... but will simulate as many single-phase ones as I can. Stiff systems are prevalent here.VERY GOOD QUALITY.1st one I received was used with exposed, sent it back. 2nd one I received was used and didn't work, sent it back. 3rd one arrived and works as advertised... Pain in the butt to go through all of that, but it's a decent unit. Wish it had an output display for V/Amp, but if you already have a battery shunt it's not a huge deal.Outputs ~ 40 Amp up to 28.8 Volts. Amps are adjustable down to ~ 9.Note, unit does draw ~ 10W when not in use. (Reason for 4 star instead of 5) I solved that with an resetable fuse. Pop it when not in use.I have been using this charger on my 3 solar projects at my house. It is run by a pure sine wave 2000 watt inverter. Every evening I plug in this charge to my 205 ah 12v LiFePo4 battery pack and by morning it is charged. I greatly value the amp adjustment as I have only used 10awg wire to connect to my pack. These get hot when I push above 2C charge rate. I turn it down and it is easier on everything. I have used it at the 75 amp setting through my BMS which is rated at 100 amps and the charger works like a champ. This is a workhorse charger. The auto switching from 12 to 24 to 12 works great. Recommend always plugging into the battery before switching on. It autosenses the voltage and adjusts.Great product for us living off grid I have flooded deep cycle batteries and was getting poor results changing with today's smart chargers, I will be upgrading to lithium ion phosphate batteries shortly and this charger does them all.I had a few questions about how to properly install to parallel batterie bank and they had all the answers. Thanks to this companie who cares and answers their phone. northern ontario canada ??.On 24volt system it puts out 41 amps , Amp draw is 0.12-0.20 This is normal Thanks Aims ONE YEAR LATER IT STOPPED WORKING WITH NO ONE TO HELP WITH A 2 YEAR WARRANTY ????WTF AMAZON WTFExcellent warranty