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Furstratingly, I have this same issue. I have a 2012 Evora S that sits in th a garage on a trickle charger most of the time. I have had to replace the battery twice in the last three years. The trickle charger works for a few months, then I return to find a flashing red light and a completely dead battery. Have no idea what is causing this, but it's driving me crazy. Hope someone has some ideas on the forum.
Not sure that I understand. All "trickle" charges are not the same. Battery Tender contains a chip to carefully monitor when to charge and for how long.

The trickle charger on my generator always was on and killed the battery in 4 years.

So, what kind of charger have you? Smart or dumb?
 

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Furstratingly, I have this same issue. I have a 2012 Evora S that sits in th a garage on a trickle charger most of the time. I have had to replace the battery twice in the last three years. The trickle charger works for a few months, then I return to find a flashing red light and a completely dead battery. Have no idea what is causing this, but it's driving me crazy. Hope someone has some ideas on the forum.
That's why I switched from Battery Tenders to Battery Minders. I had Tenders on 6 vehicles, but still had batteries going bad. Minders have desulfication and temperature compensation. There are other, better, battery maintainers out there, it's just the Minders are pretty decent at a similar price point of the Battery Tender's.
 

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I've used Battery Tenders since 1985. Not had a failure yet. My batteries last a long time. E.g. Elan went 10 yrs.

Let's see answer from Kmo before looking for conclusions.
 

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I've used Battery Tenders since 1985. Not had a failure yet. My batteries last a long time. E.g. Elan went 10 yrs.

Let's see answer from Kmo before looking for conclusions.
Appreciate all the posts. I am using a Tender. I am on the second one, and have killed at least two batteries in three years. Seems counter intuitive that a Tender versus a minder would have that potential negative side effect given the likely use case = long term storage. However, I think I may have found the culprit. I run my cord under the deck lid and gently close the deck lid on the cord without latching. In examining it the other day, I think the light in the cargo area under the deck lid stays on unless the latch closes. If true, the constant drain could outrun the current from the trickle charger, leading to a fully depleted battery. I made sure the latch was closed completely last week. I will check this week and report back to see if that addressed the issue.
 

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I'm in the same boat as glb above.

I currently have 15 Deltran Battery Tenders on various car and boat batteries. Most are older Battery Tender Plus, but I also have a few older jr.s and even the newer 6/12V Plus units. Some of my Tenders are 10-15 years old. I have never had a Tender fail, although my brother had a 10 year old jr. fail.

I previously kept an Optima yellow top deep cycle I had in a street rod on a Battery Tender for over 10 years and it was still working fine. My Evora gets put on a Tender everytime I pull in the garage.
 

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Appreciate all the posts. I am using a Tender. I am on the second one, and have killed at least two batteries in three years. Seems counter intuitive that a Tender versus a minder would have that potential negative side effect given the likely use case = long term storage. However, I think I may have found the culprit. I run my cord under the deck lid and gently close the deck lid on the cord without latching. In examining it the other day, I think the light in the cargo area under the deck lid stays on unless the latch closes. If true, the constant drain could outrun the current from the trickle charger, leading to a fully depleted battery. I made sure the latch was closed completely last week. I will check this week and report back to see if that addressed the issue.
Yes, the light stays on if hatch not fully closed/latched..... OR manually close latch in trunk lid, shutting off lights, and allowing trunk lid to "rest" closed but not latched, precluding trapping cord......another option is to replace trunk lights with LEDs....the standard bulbs will draw much more and may be your culprit when latch not in closed position
 

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Appreciate all the posts. I am using a Tender. I am on the second one, and have killed at least two batteries in three years. Seems counter intuitive that a Tender versus a minder would have that potential negative side effect given the likely use case = long term storage. However, I think I may have found the culprit. I run my cord under the deck lid and gently close the deck lid on the cord without latching. In examining it the other day, I think the light in the cargo area under the deck lid stays on unless the latch closes. If true, the constant drain could outrun the current from the trickle charger, leading to a fully depleted battery. I made sure the latch was closed completely last week. I will check this week and report back to see if that addressed the issue.
I use a "remove before flight" key ring in the tailgate switch to turn the light off. Sorry for the dyno picture, but it's the only one I have on me, haha!
1257579
 

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^Interesting you say that. I pulled out of my garage yesterday but forgot to unplug. Amazingly my Ctek charger still lights up after being dragged behind my car at 70MPH down the freeway. That doesn't make me feel any less an idiot for driving around dragging the thing 15 feet behind my car all the way to my destination.
 

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I've observed that the Battery Tender logic might be a little too smart for something with a high parasitic drain. I have two Battery Tenders - a junior (0.75A, if I recall) and a standard 3A model. Both are in constant use. Both do a fine job keeping a disconnected battery up to snuff, but I've observed on my Elise that the Junior really struggles to keep the AGM battery in the Elise topped up while it's connected to the car. The standard 3 amp tender will top it up, but doesn't trigger another charge cycle very quickly if the battery discharges from parasitic loads while plugged in.

I suspect that's what is killing the batteries in your Evoras. The Tender gets the battery up to 14 or so volts, then goes into a wait state, and doesn't start charging again until the battery voltage is so low that some damage has occurred. A dumber charger with a strictly voltage sensitive top up function (I have a 10 Amp Schauer Ship and Shore like this - maintainer mode kicks on at something like 12.8V and off at something like 13.8 V irrespective of anything else) would do the job better. Also, I know that AGM batteries have different topping voltage requirements than FLA batteries do. Be sure to get one that knows what an AGM battery is.

I kept a FLA marine battery in the basement topped up with the Schauer for years - had it on a timer so that it would only turn on for 30 minutes once a day. The battery voltage always fell down below the turn on value by the time the next 'on' cycle started, but if the battery was really full, it would just push the battery up to 14 volts quickly and then the 'fully charged' light would come on and charge current would go to zero. If I'd used the battery recently (it was hooked to a 2KW inverter), it would put 3-5 amp hours into it every day until it was full. If I'd heavily used the battery, I would just switch the timer on manually and then come back the next day and set it back to timed switching.

Conclusions:
  • I wouldn't use a Battery Tender Junior on a car - the parasitic loads are just too high.
  • A timer switching the battery tender on and off daily (say a 2 hour on cycle) will trigger the 'top up' mode on the tender and will probably resolve the discharge issue you're seeing.
 

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^Interesting you say that. I pulled out of my garage yesterday but forgot to unplug. Amazingly my Ctek charger still lights up after being dragged behind my car at 70MPH down the freeway. That doesn't make me feel any less an idiot for driving around dragging the thing 15 feet behind my car all the way to my destination.
This is why I use the key ring to "close" the switch. That way I can leave the hatch fully open and won't drive away before disconnecting.

I try to implement as many idiot checks for myself as possible, because I always find a way...
 

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^Interesting you say that. I pulled out of my garage yesterday but forgot to unplug. Amazingly my Ctek charger still lights up after being dragged behind my car at 70MPH down the freeway. That doesn't make me feel any less an idiot for driving around dragging the thing 15 feet behind my car all the way to my destination.
Sounds like you need a magnetic battery charger connection ;)

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Luckily these cars usually come with a Lotus branded tender. I'm assuming that one should be up to the job.
 

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Lotus branded = Deltran btw. The Op fessed up to the cause of failure. Wasn't closing the latch so battery was under more load than the charger gave back which also means he/she never checked to see if light went green meaning charged...
 

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So, problem solved. Per my prior post, I suspected that the cargo area light was staying on and the parasitic draw was out-running the Tender, thus, depleting the battery. As a test, the last time I left the car, the battery was at 12v and I put the Tender on, making sure the deck lid was fully latched. Came back a week later and the battery is fully charged, and the Tender has a solid green light. So, make sure you deck lid is fully latched or the light will stay on and you will have a dead battery, even if it looks closed! Thx to everyone for the various posts.
 

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So living here in New Jersey and temperatures at 30 degrees in mornings and not having heated garage the oil is little heavy for starting.
But having Battery Tenders approx 4 of them and most are probably 15 or better years old and all of them are 1.25 amps..
Yikes time flies and you forget how long you have had things..
So with old Battery Tender/Plus on Evora for last few months and going out at times to start and drive it ,
It was very hard for Evora to even turn over these cold days and would click click and then turn over and start and few days no start.
So purchased the Schumacher SC1304 that has 3 amp maintainer and not the 1.25 amp Battery Tender is and today at 30 degrees
and went out to start..
Wow what a difference in how Evora starts..With authority ...So now have to wonder if 3amp is the reason and is that what is needed
for these newer cars or vs my very old Battery tenders the reason.
So I will keep the SC1304 on..The reason I did not put SC1304 on month ago when purchased was not having quick connect plug to
remove..So will keep plastic cover off and carpeting off during rest of this winter months and make a quick connect this Spring..
 

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Sherman at Hethelsport's magnetic charger kit is first rate and great value for money. I made a bracket to install it because I didn't want to drill a hole in my bodywork. The magnetic charger detaches if you drive off with it connected. I've had good luck with the CTEK chargers/conditioners. I have their MXS5.0 charger on my Evora.
 
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