What should the output of a trickle charger be?

D

dwasifar

Joined
Jan 16, 2021
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We put a car in storage over the winter with one of those little 1A trickle chargers on the battery to keep it topped up.

It didn't work. The battery went dead, and I'm trying to figure out if it was operator error or something wrong with the charger.

It's possible I chose a bad ground point when I connected it, but when I metered the output of the charger expecting to see 12VDC, instead I saw what looked like pulses. Is that normal?

I reconnected the trickle charger to the battery and the red "charging" light came on. 24 hours later, the battery reads 2.7 VDC. If there's nothing wrong with the charger, then the battery is toast, but I'm not sure how to determine if the charger is OK.
 
Most automatic chargers will not charge a battery that is run down to zero. Test with a known-good battery. Within a few minutes, the voltage should come up to about 14 if the battery is already charged.
 
If your 12 volt battery is reading 2.7 volts, then I would say it's toast. Whether or not it was the fault of the charger or the battery, who knows.
I use a 1.25 amp Battery Tender to keep my car batteries charged and it works well. From what I can tell, it will slowly charge up to 14 volts and level around 13.2-5 volts to maintain it. I connect directly to the + and - terminals on the battery.
I've also used a Battery Tender Jr, which only output .75 amp and that worked fine until the charger failed. The original Battery Tender is built to last much longer than the Jr according to Deltran, the manufacturer.
Your 1 amp charger is sufficient, I think your battery simply failed. But, test the voltage output on a good battery while the charger is connected to see what it does and verify if the charger is doing anything.
 
From this I'm going to assume A) Operator error caused the battery to not be topped up, and B) The charger is probably fine but won't revive a battery that's gone down that low. I suppose I could jump-start the car and see if the charging system will bring it back to life. Can't do it right now, though; don't want to leave the car running unattended in the driveway.
 
Just buy a new battery, it is not worth the risk of killing your alternator and having to replace that as well.
I drove my Mazda3 for a couple of days on a dead battery (I believe it died from an internal short as it would not hold a charge) and a few days after I replaced the battery, the alternator stopped outputting voltage. I am confident that driving on a dead battery ruined the alternator.
Lesson learned, replace a weak battery before it becomes dead-dead.
 
I always disco the BAT GND cable when put up for charging. With modern ECU, I guess you dont want to to that.
I did have two trickle chargers fail over winter in FL over the years.
I think the last one was expensive , a Stanley or something. Toast.
 
CharlieJ said:
Just buy a new battery, it is not worth the risk of killing your alternator and having to replace that as well.
I drove my Mazda3 for a couple of days on a dead battery (I believe it died from an internal short as it would not hold a charge) and a few days after I replaced the battery, the alternator stopped outputting voltage. I am confident that driving on a dead battery ruined the alternator.
Lesson learned, replace a weak battery before it becomes dead-dead.
Click to expand...
I agree.
I bought a Voltage Meter that plugs into the cigarette lighter.
It's handy for checking the battery and alternator while driving.
Engine OFF .... 12V (battery)
Engine ON .... 14V (alternator)
 
Last edited:
Is it a charger that puts out a constant 1A regardless, or a maintainers? I got a 0.75A Schumacher maintainer for my parents, since they lost everything else I got for them, and they leave their car un the garage for a month when they go on vacation.

Automatic maintainers using firmware are different. They need to sense that there's a certain voltage, or else they won't charge at all. They're meant to maintain a near full battery, or at least one that's fairly well charged. They may also have a timeout where they cut out if they don't sense it's fully charged - maybe 12 or 24 hours. But if it's working correctly, one should top off the charge until it's full, then monitor and start charging again when the voltage reaches a certain threshold. A chart of the voltage over time should look like a sawtooth with a fairly quick ramp up, then a slow drop. Of course it's complicated by all the electronics that draw current, but that should be fairly low unless regular headlights are turned on. If that's done, no maintainer can keep up. 2 55W halogen bulbs draw a little less than 10 A.

I have an old analog maintainer, and that only has reverse protection. I'm not quite sure how it works, but I don't believe it's constantly putting out current when full.
 
y_p_w said:
I have an old analog maintainer, and that only has reverse protection. I'm not quite sure how it works, but I don't believe it's constantly putting out current when full.
Click to expand...

Ideally it has voltage regulation so it floats the battery at around 13.8V or so (probably 13.5V or even as low as 13.2V would be better).

Some (poorly designed, IMHO) trickle chargers are not voltage regulated and can output 14V or more when the battery is fully charged. This is not what you want, the extra voltage at full charge will just make the water in the battery turn into hydrogen and oxygen (called "gassing") and with many newer batteries not having any way to add water...you can see the problem.
 
Thanks, guys. I took the advice about not risking the alternator, and bought a new battery, an Interstate AGM. Group size 35s are hard to come by right now, I had to drive an hour for it. :)

Lesson learned.
 
brianl703 said:
Ideally it has voltage regulation so it floats the battery at around 13.8V or so (probably 13.5V or even as low as 13.2V would be better).

Some (poorly designed, IMHO) trickle chargers are not voltage regulated and can output 14V or more when the battery is fully charged. This is not what you want, the extra voltage at full charge will just make the water in the battery turn into hydrogen and oxygen (called "gassing") and with many newer batteries not having any way to add water...you can see the problem.
Click to expand...

I think separation of water is hydrolysis. I only remember the word because of talk about using electricity to produce hydrogen gas.
 
2010Civic said:
Pick up a Noco Genius 1. I've used these for multiple years on multiple cars and they work great. Very high quality unit.
Click to expand...
Yes, they actually offered to sell me that at the Interstate store. I had a 20% off coupon, I should have taken it.
 
now there's a new generation of batteries.
Make sure U treat
the AGM and lith ion (even the gell) differently that the ol flodded (esp
when charging or maintaining). The noco is a good idea as it has capacity
to switch (one must do it manually) between these different systems.
 
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