Battery charger faulty or normal?

user11

Newly Enlightened
Joined
Nov 15, 2015
Messages
29
I have a 35Ah sealed AGM battery which doesn't get a lot of use, maybe 20 times per year for a trolling motor. Never run flat. Usually it charges up to about 12.9V.

I'm using a branded 2.5 Amp 3 stage charger. Yesterday I ran it down to about 20% by my estimate, it was down to 11.95V with no load.

It's been on the charger for about 22 hours and the orange 'charged' light did not come on. You'd think it would be fully charged by then allowing for say 2Amps per hour. However it likely reduces the current so I can't really tell other than by the Voltage.

Anyhoo I put a Fluke 101 Voltmeter on the charging terminals while charging to see how much Voltage the charger was pumping in expecting it to be showing around 14V to begin and then expecting it to drop down. However it began at 12V and just kept gradually rising. After a few hours it was reading 12.3V. So it appears that it's not reading the Voltage coming off the charger but simply reading the Voltage of the batter. Is this normal would it be expected to just show the battery Voltage and not the Voltage flowing off the charger.

The battery was not hot or even slightly warm after 22 hours. I removed the charger and the battery was showing 14.6V I then plugged a 12V low powered pump onto the battery to remove the surface charge to get a better reading. After removing the surface charge the battery still shows 13.5V or 13.2V under load.

Does this sound normal? this is the charger https://youtu.be/pZnJTqLxans?t=24s it's out of warranty btw.

P.S. I seem to remember that when plugging it into a depleted battery last year that the Voltmeter would read 13.5V at the charger terminals when charging which is why I found it strange that it was only reading 12V to begin with this time. Although it has seemed to charge albeit over 13V with load!

Is there some way to test the charger.

thx
 

user11

Newly Enlightened
Joined
Nov 15, 2015
Messages
29
I think I have solved the problem which is that the problem is that I was using this for a 12Ah battery where it works as expected, but it works differently for a 35Ah battery
 
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