Hi, I am building a power pack for a laptop... reason being we make recordings on the laptop of sermons, but the power in the building where it is done is very "Noisy"? resulting in terrible recordings. What we did was using a 6V and 12V car battery in series, connecting the original power to the batteries and getting perfect(clean DC) power into the laptop, which results in beautiful recordings. This is a temporary solution. I am planning to use 3x 6V batteries in series, a few diodes and the input and output connectors. I have attached a picture of a drawing i planned, this may be incorrect in which case please let me know. I am open for any suggestions.