battery alternatives for Nagra 4d

hello..
wondering if anyone out there has been able to figure out an alternative to the battery issues with the Nagra machines?
Just read another posting talking about building PSU's for them, but I'm trying to figure out an alternative to the battery situation; needing 12 D batteries, the rechargeables are so expensive.

anyone know why there's any reason why I couldn't use an 18v battery from a cordless drill?
the nagra takes 12 1.5v D batteries=18v...

any thoughts, recommendations?

thanks!