to add a little more speed and power to my linear actuator

i have been talking to a few people about it and i have discovered i cant use it in the following way

battery-speedo-booster-linear actuator

this is becuase the polarity will reverse and blow the booster up

however what will work is (i believe)
battery-booster-speedo-linaer actuator

aslong as the speedo can take the higher voltage

so im looking for something that will up the voltage

so if anyone can help iei has one to sell, knows of place to buy or maybe my idea above is incorrect
please post here

cheers alex