Keeping 57's battery charged thru cig lighter?

A friend of mine has a 57 in his garage and he has no room to lift the hood to get at the battery to hook up a charger to keep the battery up, he was wondering if he could use one of them cigarette lighter type of units to keep a charge in his battery. I figured best place to ask that would be here, I don't have any experience with the older cars. I know you can use little gadgets to keep computer memory alive plugged into the cigarette lighter, but don't know about actually charging the battery. Any thought welcome guys!

Most parts stores sell battery maintainers he can pull car out and install it. Then he can run cord thru the grill. I have one on my diesel tractor as I don't run it in the winter. If you use one check battery water every six months.

If it was my '57, I wouldn't do it just because of the age of the wiring. But here's a link if he wants to try it on his.

http://www.amazon.com/Battery-Tender-Deltran-Cigarette-081-0069-5/dp/B003CJ927I

Here's another link that makes it sound more promising.

http://www.autogeek.net/battery-tender-lighter-adapter.html