I have been using a Battery Tender Jr. for quite a while. It seems to do the trick but has never been very consistent in the time it spends "charging" and "maintaining". Sometimes it will go from flashing green to green in 5 minutes, sometimes it takes hours. So with a little digging I was able to find some algorithm charts on the Battery Tender Jr. and BatteryTender Plus. Looks like the Junior does not even have an absorption phase. It just applies voltage until it reaches 14.45 volts then goes into float voltage of 13.2. The Plus model goes up to 14.4 volts then holds it there for several hours until the current drops due to internal resistance of the battery rising. Just like what we used to watch for on the ammeter of our old dumb chargers long ago. I have always suspected, and from reading lots of opinions on the web others do as well, that the Junior never really fully charges a battery. I have called Deltran in the past and it has been very frustrating because they know less about their chargers than I do and that's not saying a lot. Now I know a lot of people will say that a maintainer is NOT a charger, it just maintains. But that is not what Deltran says about their Battery Tenders - they call them chargers and describe them as so in their marketing. The reason I was digging into this is to make sure I put a full charge on newly acid filled batteries. In the Battery Tender FAQ section, they say that the Plus model will do the initial charge on a new battery but only if it's left on for at least 48 hours, which is ridiculous. And they don't even address whether the Junior is capable of doing it. When I asked this over the phone, the guy said "I don't see why not". Real technical answer, yeah. So I put this up just in case anyone has interest.
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