I buy a new whisperer every year (on my 4th year now). I also try to charge the old ones each year. I set them in the direct sun. At night I put them under a direct indoor light source. This year they have been charging for a little over 4 weeks now. This gives them enough power to run for 7-10 seconds. As the watering season where I live is only about 4.5 months, this means that every whisperer only lasts me 4.5 months. It's a pretty expensive solution at this rate. 

Is my experience common? Has anyone gotten a whisperer to work after being stored over the winter (and I do charge then fully before turning them off for the winter)?  I assume the internal rechargeable batteries just aren't that good. Has any one had any experience changing the batteries?