Powering a system using batteries
I think you should go with 3 lithium batteries in series and for proper balance charging of batteries, you can use an off the shell 3s lithium charging circuit like this here.So you will get 4.2*3 = 12.6V on full charge and on full discharge you will get 3.7*3=11.1v out of the battery. 

So still I think your pump motor would work on 11v and ther are chances that your solanoid also work on 11v it will just draw more current then usual.