He read that information on a few sites then went with West Marine as his trusted source which suggest a panel of 1.5% in "amperage" of the 20 hour "C" rate is safe. The information is confusing for the DIY at best and there are numerous sites out there with varying formulas for no controller.. He read 10% in watts to "C" then bought a panel that was considerably less than 1.5% of "C" based on the West Advisor article....

If we follow my customers interpretation of the West Advisor statement that a panel output in current of 1.5% of 225Ah's = 3.38A (according to the West Advisor)

The Impp of his 20 watt panel was only 1.16A (which I agree is far too much, batteries agreed too)

Below is from the West Advisor and why people get confused and sometimes cook batteries:

"Do you need a charge controller?

As a general rule panels that produce less than 1.5% of a battery’s rated capacity in amp hours don’t require regulation. This means that a 1.5A panel is the largest you should use without a regulator on a 100-amp-hour battery. Regulators should generally be used any time you have two or more large panels connected to your batteries."

With winter self discharge rates so low, usually less than 5-10% of "C" for an entire winter, it is pretty hard to find a panel small enough to not need a controller.(nl)