It is unimaginable that this little thing puts out 100 amps. It is the size of a large cigar box and a tiny bit the size of my 2, count 'em 2 big 50 amp chargers previously. It will sample your battery buss and ramp up to voltage needed for charge "bulk-maintenance-trickle" 3 stage.When I connected my 8 golf cart battery bank I watched the buss voltage on my inverter ramp up to 14.6 and the 2 gauge wire I connected from this charger to the buss got a tiny bit warm. Huge amperage. I bought it for rapid recharge of the battery bank from either my Kohler industrial standby power plant, or my Honda 2000 portable generator. There was a lightning strike induced substation outage recently and I used my battery bank for a couple hours and then ran this charger off the Honda 2000 and the Honda was definitely under heavy load from this unit. The fans will come on soon after a full load and it keeps cranking out the amps. Seems to be a very good unit and being an electrical engineer, I don't see how it puts out this kind of current from such a small form factor.

Ordered this item since it is advertised as a 4 stage charger, which in the typical industry language nowadays means a 4 Stage Smart (Automatic) function. It is not, it is only a 3 stage smart charger, although I did not physically verify that. If you expect to get an automatic equalize charge from this, it will not (per the manual) do that, yet the Battery Equalize function is one that is essential to battery maintenance and longevity.
The manual says it is a "100 Amp and 3 Stage Charging Option" on the front. Inside it has a section called "4 Stage Charging Option Description" which is very poorly written. What I can gather from it is that what they are calling the 4th Stage is a switch which you must manually access and then using a digital volt meter adjust to the value desired. That is worthless once the unit is installed as typical for an RV as it is usually inaccessible or at the best difficult to access. This may work fine if you don't want the stated functionality, but I am returning it and will purchase from another seller that clearly implements the automatic 4 Stage function.

Not a fan. The cooling fan is quite loud. I am hesitant to believe the power output. I have tested my batteries voltage, and it never seems to be over 12.8. A little info. I have charged these with my portable 40 amp charger, and they charge fully to 13.1. This is not what I would call a smart charger. It does not desulfate. It really has only 3 charge stages. The instructions are absolutely useless. This could be a better charger than I think, and just don't have it adjusted correctly because the instruction are so poor. Don't know if I would recommend yet.
EDIT: Added a star. I re-adjusted the unit, it seems to be working well.

This thing is so much better than the 1983 model I replaced. That one was quite literally a block of wood with copper wire wrapped around it. I've never seen anything like it! This charged my batteries right up within an hour using my 2000 watt inverter generator. I boondock all week near my work then stay in RV parks during the weekend. I was having to run my generator 5-6 hours just to charge my batteries enough to make it through a cold night. And this was with a brand new furnace that's super efficient. Very happy with my purchase. On a side note the instructions show how to adjust voltage output and I did follow them. If not with only 2 batteries I was only getting a charge output of 13.5 volts instead of the recommended 14.6. Also some reviews have stated the fan noise being loud. This is accurate however then fan does not run all the time. We will see how bad it is when I stay in an RV park this weekend. Hopefully it isn't too much of a concern.

VERY upset at the durability of this product!!!! Bought the PM475A nearly FOUR months ago, and now, it doesnt work!! Completely dead. Installed unit on AUG 23, 2017. Checked ALL fuses, checked power cord....120VAC going into the unit and ZERO coming out....Nothing! When it was working, it did well. But this reliability and durability issue is COMPLETELY unacceptable!!! The OEM unit lasted 14 years and this one lasted 4 months.

I am going to report this product to the company. I cannot say anything (for now) about PowerMax, the company that makes this product, but if they do not back their products when I ask for a return, I will recommend on websites to avoid this company.

!!!!!!!***PLEASE******READ******UPDATE***!!!!!!! >>>>>>>>> 13 JAN 2018
After calling PowerMax and explaining my situation, they were completely willing to fix the problem!! They were not only understanding, but they were very quick in sending (UPS 2-day) a new PowerMax replacement immediately! Totally impressed!! Would do business with this company in the future!! I respect people who stand behind their products!!

I will update in a few months as to the reliability of the product.

Thank You PowerMax for your exemplary professionalism and service!!! Company gets 5 Stars, 3 stars for product.