[AT] Solar battery charger setup

[Bill Bruer]

I recently picked up one of these 1.5 watt solar battery chargers on sale at 
Harbor
Freight for $14.99 -
http://www.harborfreight.com/15-watt-solar-battery-charger-68692.html

The manual says it needs an external voltage regualtor to prevent
overcharging.  There's no indicaction of that requirement on the packaging.
What's the best (cheap) way to set this thing up so that it can be left
on a battery for indefinite periods?  Harbor Freight has a 100 watt 
regulator -
http://www.harborfreight.com/7-amp-solar-charge-regulator-96728.html
that will also allow you to power a tool but costs $25.99.  Kind of defeats 
the
sale price on the charger.

My main use will be to keep the battery hot on my IH 686 tractor with a
D312 engine.  However, I would like to mount the panel and regulator on a 
light
frame that can be moved to any piece of equipment where it may be
needed.

Bill Bruer
Murfreesboro, TN