Best Solar battery maintainer for non-daily driver

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Google "vw solar battery maintainer"
I have found the cigarette lighter version on ebay years ago. Works flawlessly.
There is also a can bus version for the vehicles that cut the connection to the cigarette lighter
 
I've been using the cheap HF and Northern Tool ones, they've been doing well, even on dual battery diesels, as long as the battery(s) are fully charged before parking them. Connected straight to battery with the little clips.
 
I've used a handful of different ones and I think in general, they're all about the same. I'd buy based on price, connectivity, mounting style and wattage.
 
Is the 5-watt battery tender solar charger a good quality one? One thing I do like about that one is that it has a built in controller. Is that important?(from what I understand it is ideal to have one)
 
To be honest, for a solar charger in that range, a controller isn't really necessary, I don't think that you'll run any risk of overcharging the battery. Let me try calculate this just for fun:

Let's say your battery is roughly 40Ah, with a self discharge of 5% per month, or 2Ah per month, or .0666Ah per day. The vehicle will likely draw some power constantly, let's say the parasitic drain is 0.05A, or 1.2Ah per day, for a total of 1.2666Ah per day.

The solar charger, on the summer solstice in Pensylvania will receive 15h of sunlight, and assuming it's perfectly pointing at the sun the entire time with a 100% charge efficiency, the .27A charge current will recharge 4.05Ah of capacity. Arguably, you won't get anywhere near that power.

I've used the cheap-o $15-$20 5 watt chargers with no issue. I think the only thing to take note is that it has a built in blocking diode so that it doesn't discharge the battery when off, most of them do have it.
 
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