"Memory keeper" -- any info, please

Every year I spend the summer across country. I remove the car battery and store it indoors. However, I’ve been having problems with the practice upsetting onboard memory.



When it was just radio settings and power seat settings, it was an annoyance.



This year, however, I needed to have my car smog checked as soon as I returned in order to re-register it. It failed.



The mechanic told me that it was because the lack of power had upset the chip that regulates the emissions. He said it would reset itself after about 4,000 miles of driving. I don’t drive very much and that’s just about as far as I would go before I leave town again. And I can’t drive that long with an unregistered car.



I’ve heard there are “memory keepers” that you can plug in to the power port to maintain all your electronics while the battery is disconnected.



Does anyone know about these? Where to get them? How much do they cost? Do they work? And would they last six months. I can’t imagine the onboard memory consumes that much power.



Thanks.

Rather than go the memory keeper route (usually just a 9 volt battery attached to the cigarette lighter to back-feed power to the fuse box while the battery is disconnected… not the greatest invention, in my mind), might I suggest leaving the battery in the car and using a trickle charger connected to the battery to keep it topped off? You can pick them up for $20-40 at most parts stores, they’re just a little box that has terminals that attach to the battery, plug the box in to an extension cord, tuck it away somewhere under the hood, and let it go. When the battery voltage dips a little, it will top it back off, until you get back to the car.

what mrjosh is referring to is this:
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=42292

as another alternative; http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=41144 there are solar panels you can buy for about 40 or 50 bucks. they sit on the dash, and trickle charge the battery.

i personally would NOT get something that plugs in to household current, and then LEAVE unattended. that sounds like a recipe for disaster. the solar panel idea is low voltage, and would seem much safer. (but this is supposing the car is not ina garage!? maybe there is a south facing window nearby to put the solar panel in though?

one more thought: the solar panel, or any other device that plugs into the cigarette lighter must use the secondary power socket. most modern cars have the cigerette lighter on only when the key is turned on. but the power plug (usually marked differently than a cig lightr) is on all the time. BUT you must test it before you depend on it.