Hello,
I have experience in creating various web applications so this battery calculator should not a problem.
Unfortunately I only have a very small amount of experience in WordPress so I wouldn't be able to help you in that department but I can make a simple HTML/Javascript/CSS form that will give your users the battery calculations that are required.
Please note that my bid only includes the calculation form itself along with a simple design. Part of your project description makes me question whether you need an entire web page or not, please tell me via message if this is the case and I will alter my bid.
Regards,
Josh.