I use the Battery Minder. I have two - the 12112 (1 amp) which I've had for over ten years (and may have been discontinued and replaced with another model) and the model 2012 (2 amps) which I purchased a year and a half ago when I needed to charge three batteries (two car batteries and one mower battery). Both have worked flawlessly. I have trickle charged two batteries in parallel with each unit. My Dad and brother both use the Battery Tenders and I haven't heard of any problems there. I'm pretty sure my Dad has the Battery Tender Jr which is fine for a single battery.
I was curious myself. I knew that the plus has more amperage than the Jr. but found this summary after a little searching
In the analysis of buying a Tender Jr. vs. a Tender Plus, the main issues are time to full charge, battery size, & parasitic draw. The Tender Plus (1.25) will get the job done twice as fast as the Tender Jr. (0.75). Both now are similar architecturally, save it be the charging power & lack of temperature compensation on the Jr. They both are 4 stage, both have the same sophisticated computer chip technology running the charging process, etc... I spoke to The Deltran(The Manufacturer) customer service department on 3 different occasions, making sure I had the facts right. The first 2 times I was misinformed about the temperature compensation issue. I am editing this review to be accurate as of today's date of 12/01/10. Because The Plus will bring a battery to full charge twice as quickly as The Jr. will, The Plus has a much better chance at overcoming a parasitic draw on your batteries power.
It sounds like the Jr is fine for most applications. Just no temperature compensation and lower amps. In the winter I usually pull my battery and put it in the basement where the temperature is in the 60 's vs. the garage where it is <40 F.
Interesting, I'm gonna need to get one before winter for sure,even though I start it often, it's kinda embarrassing to say, I've not had my car on the (ROAD) since May/013.
I have used the jr. for the past 3 years. My car is in an unheated garage and the weather here in Ontario is cold. Have had no problems with battery or starting car. Just plug it in and basically forget it until Spring.
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Reference:
http://www.twtex.com/forums/showthread.php?t=55767