I just learned these existed.... just wanted to let others know too. I used to keep my batteries on a battery tender in the winter. I just bought a couple of these off ebay for $15 ea. There are 2 kinds.... the older ones with cigarette plug were 3.2 watts, and the newer ones with the OBD plug are 4 watts. I got the 4 watt ones, with the intention of splicing on some battery charger style clamps. Then stick it to the garage window with the suction cups. If you were looking to buy a battery tender, one of these off ebay will likely be cheaper to buy, and free to run! :thumbsup:

This one's just an example.... I have nothing to do with the seller...
http://cgi.ebay.com/ebaymotors/Genuine-VW-solar-trickle-charger_W0QQcmdZViewItemQQcategoryZ46093QQihZ013QQ itemZ230117133801QQrdZ1

You have the right idea to keep your battery charged inbetween use esp considering car batteries can loose up to apporx 3-4% charge wkly just from sitting/in non use periods.

Many people dont bother to do this and wonder why the have hot start issues esp with a high comp BBC on a hot day.

But infotunately you may not be aware the 4 watt solar panel you using is not enough juice to keep a lrg std pass car battery from sufating over time which is what kills them. Yes it should do the job on a small motorcycle or mower battery but not a 4x-5x larger car battery.

Yes i know the mfg says it will do the trick for a std lrg car battery bit in reality 4 watts wont cut it and cant really do the job.

I use 1.5 AMP float charger that will charge the battery if it needs it to a full charge then it cut bact to a lower float carge rate to keep battery chemically more active to prevnt sulfation of plates which is what kills batteries over when sitting with out chraging in our classic cars. Then if the battery voltage drops back to a certain voltage the charger kicks back into full 1.5 amp charge rate untill its fully charged again.

But these small 1.5 amp float chargers are not designed to fully charge a full size car batery in a few hrs,10-20 amp chargers are made for that application.
1.5 amp chargers take a long time(days if the battery is very low or almost dead) to fully charge a car battery. These 1.5 amp float chargers hardly ever cause the electroilite to go low when using them to keep a battery charged when not in use or for wks inbetween use of a classic car even in season for driving. But just to be safe i periodically check the battery lvl and if its below the plates i would add DISTILLED WATER ONLY/NOT TAP WATER WITH MINERALS,SALT,ETC IN IT which can prematurly kill a battery.

I have used a float charger for all the time my car (and motorcycle) sits inbetween use and i have gotten a lot of yrs out of my classic cars batteries. 13yrs on the 1st battery & 12 yrs on the 2nd battery before i replaced them & have 6+ yrs on the Delco repop i am currently running. (I have owned the same classic car since 1978 which is why i was able to get this kind of consistant test info on extending car battery)

And note,that when i replaced the 1st 2 batteries they still started my 10.0 comp 396 BBC when hot,i just couldnt trust them any longer because they were so old and i didnt want to get stranded some day if they failed which is why i replace them when i did.

These small 1.5 amp float chargers dont use much elec at all esp since 99.5% of the time they are in the low maint /float mode. But this lower float mode is still at a higher amp rate the the 4 watts your getting from the solar panel thats really only good for maintaining at best an already fully charged much smaller bike or mower battery IMHO.

Scott

Scott, interesting info. I have a 1A battery tender as well, and it works fine - I definatly don't plan on getting rid of it. To be honest, I started researching solar power for other uses, when I discovered these. I know they aren't very powerful, but I talked to a solar technician about using a couple of these to keep a much larger battery topped off, and he said they'd work ok. More would be better, but 2 of them in parallel on my 110A/hr AGM battery would keep it maintained. They would be hard pressed to charge the battery if it's very low though, just able to maintain full charge. So, I decided they would be too small for my large storage battery.

But, based on that info, I'd assume that just one would work ok to maintain the 55A/hr yellow optima in my chevelle. VW used them to keep their new car batteries topped off on dealer lots, so should work for me in the same application as well. However, I live in a less than full sun environment, so I planned on putting 2 of them on the chevelle.... if a little power is good, doubling it is better, right? :D

I know they aren't the end-all battery maintainer, but I figured somebody might have a use for them. For ex, at a car show or something with your radio on/engine off, all you do is plug in the panel (or several) and charge away. Anyway, for solar panels for any use, these are the lowest $$/watt I've seen....you'd need a lot of em to do anything significant, but they're cheap.