[stevet]

I use a Battery Tender Junior (model 021-0123) for my motorcycle batteries. It's output is 12 volt and 750ma. One time I put it on the Fiat's battery and it demonstrated that it is just too small of a power supply to top off that comparably huge battery (vs. the motorcycle batteries). It was in the charge state for several hours without ever showing a full charge. The car had been driven quite a bit previous to that occasion (and has never had a charging system issue, nor problems starting), but on my little MC batteries the Junior indicates a full charge within 10-30 minutes.

I see the Battery Tender model 021-0128, which has a 12 volt and 1.25amp output, 50ma higher output than the BT Junior. ($45 at Amazon.) See them both, and more, here. They are the first two on the list.
http://products.batterytender.com/Chargers/?_ga=2.89882459.133582828.1507864563-348856958.1507864563

Is the 12v/1.25amp unit going to suffice as an occasional "maintenance charger" for the big Spider battery? I will not leave it connected for constant "smart" charging, instead installing the charger every few weeks for the period of time needed to indicate a full charge. There are other models for 12v systems that put out 3 to 5 amps, at a higher cost as well.

Thoughts, experiences, or ideas?

Steve.

 

[toooldtocare]

I use my Abarth as a pleasure car, 5 miles to the golf course, 3 miles to have lunch, etc. As a result the battery never comes to full charge (12.8 volts), so I use the standard Battery Tender to top it off every month or so. I monitor the battery and when it reads about 12.4 volts I connect it. By the next morning it is always fully charged. I have a Battery Tender pigtail connected to the battery to make it easier to connect it. I’ve done this for years on my other pleasure cars.

Wayne

 

[ameridan]

The Battery Tenders are designed to leave connected to your battery, so I would stick with the Jr. and just leave it connected to the Spider battery, unless you want to keep your strategy of occasional "top-offs". Frankly I'm surprised that it "tops off" your MC battery so quickly, as that is the job of a battery charger, rather than a trickle charger, as I write about in my blog article. They must be almost fully charged to begin with.

Your strategy (occasional top-offs) works, but you need actual battery chargers if you want the batteries at full charge in an hour or two. Battery tenders are for those that want to forget about the batteries for the winter season as an example and not worry about overcharging.

 

[frankmar]

When I winterize my Abarth 4 months in the end of November, I install the battery tender 3.0 A, That's what I found at costco(cheap price). Then when I go south in winter for 5-7 weeks, when I get back I connect my 1A motorcycle battery overnight on my SUV and next day battery will be well charged.

 

[stevet]

I just ordered the Battery Tender Plus model 021-0128 (12V, 1.25A) from Amazon, $45. Ends up a friend of mine uses this same one to maintain two boat batteries (a deep cycle trolling motor battery, and a standard outboard motor battery) and a lawn tractor battery.

I'll continue using the BT Junior just for the motorcycle batteries.

https://www.amazon.com/Battery-Tender-021-0128-Maintain-Damaging/dp/B00068XCQU/ref=sr_1_2?s=automotive&ie=UTF8&qid=1508040782&sr=1-2&keywords=battery+tender+plus

Steve.

 

[SpiderHammer]

When I've stored my Mustang in the past - I've removed the battery and stored it inside the house in the basement ( so it doesn't see freezing cold temps) and I've been able to simply put the unit back into the car and not needed to charge it, although I do have a charger in the garage just in case - I actually had already had to have the dealership replace the Spiders battery ( 3000 km) as it wouldn't hold a charge at all

 

[zvezdah1]

Battery tender plus, if you don't drive on a regular basis and car sits for weeks on end just leave it plugged in all the time.

Been using them for decades on motorcycles with no ill effect.