These are 1.5 watt solar panels , and I have two for daytime charging. Much better than having to unplug the batteries to bring them in all day to charge then carrying them back out, very practical.
I picked up a couple solar panels to use in charging during the day. Watchdog is low power during the day and shouldn't take much to charge the batteries. 18 watts charge the batteries up from a night of use after about 3-4 hours. So solar charging is within the realm of practically achievable.