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Hagerty Employee

Piston Slap: Tender loving care for battery tenders?

I have two cars that I don't drive very often (a BMW and a Porsche). Now that the weather has turned cooler, I encountered some battery issues. I purchased two battery tenders so I can avoid problems in the future. Is there anything I need to know or be careful about as I use these tenders?

The best thing you can do is this.

#1 buy a tender that will work with regular and AGM batteries. AGM is very common and if you don’t have one now you may will in the future.

#2 most good tenders come with a harness that you can bolt on with the battery side terminals. That way when you go to hook it up you just uncover the plug and plug in the tender.

I have several I use and the deal with tenders is not really complex. Most times it is plug and play. Checking water is for any battery that is still an open battery. Many have moved to AGM to get away from the corrosion issues with acid batteries.

The one thing with most AGM batteries they do require to keep the voltage up or they will not charge with a conventional charger, They require an AGM capable charger. This is why tenders are even more important to them to keep the voltage up if you don’t have a proper charger.



  I like the more secure and permanent use of the "harness" that hyperV6 refers to.  As a bonus, some things will actually plug into such a harness to be run on your battery power.  For instance, I have a small tire inflator that has the same type plug, and instead of trying to keep track of a cigarette lighter/power outlet adapter, I can just plug it directly into my "charging harness" and draw power out instead of putting it in.

   For the larger batteries out of my "summer" vehicles and for my trailer winch, I remove the batteries and put them under a bench in the shop on a piece of plywood.  Easier to monitor, keep clean, and do any maintenance than if left in vehicles spread all over the place.  Also ensures I'm always close to an outlet, which my trailer and ranch tractor hardly ever are.

Intermediate Driver

Occasionally putting a tender (with "desulfating") on my (now) 5 year old battery has actually improved it's performance. The once-a-year safety inspection in my state means the garage gets to "remind" you of things you might need. One year, they warned the battery was going bad. I said I would replace it once it dies. The next year the battery was in a much better state and they didn't have to remind me of anything.
Pit Crew

Read the directions. Battery tenders want to be installed on the terminals before plugging them in.
I have had better luck with the C Tec s .
New Driver

Thank you, Sajeev. This is exactly the kind of information that I was looking for.
As the other responders have indicated, I have also permanently attached the battery tender connections securely to my batteries. Now I simply reconnect the battery tenders to the cable after each use. They have been working flawlessly.
Community Manager

That is great to hear, you are definitely doing it right! 

Hagerty Fan
Not applicable

A bit late to the party but fwiw and posterity….
I have a couple of “smart tenders” that are suitable for boats and so are advertised as water-proof…and (apparently) some of the other liquids found on in my shop. The additional cost for that feature was negligible but it’s saved me a few times over the years. Just a thought.