No issues with the light. Yes, I just inserted the cells in series with the +12 volt lead going to the switch. My 3" valve was somewhat slow to open. But now it operates in about 4/10 of a second. What a difference. The motor should easily stand the increase of 1/3 voltage. That gives about an 80% increase in available torque to get the blade moving. So far, no crawling under to use the wrench or pulling the entire valve to clean and lubricate. If I run into any further issues related to the voltage boost I'll be sure to post.
Afox2012