12v Battery charger jumping up to 19v?

[SpookyGhost]

I have a NOCO Genius 1 battery charger. Right now I'm using it to charge up a test a bunch of 12v SLA batteries I have laying around from UPS replacements

I've notices that sometimes, the battery charger will spike up to 19v. Is this a charger problem, or some kind of battery problem? Here is a video

https://youtu.be/HN3CxfZJTjo

I fist noticed this when I connected it to a VERY old 12v 16ah SLA battery, it did this and I just assumed it might be normal. I came back to the battery a few hours later, and the charger was idle, and the battery reads just 1v

I plugged in a second one of the old 16ah batteries, and after a few hours same thing. Battery completely dead. Since then I've charged maybe 5 batteries with no problem. I plugged in another and noticed the same behavior. But I disconnected that battery and connected a different one, and it does NOT do it. Here is a video of that

https://youtu.be/PCHJ_AK1BSM

Am I missing something here? My main concern is that I use this charger to charge batteries in devices such as a portable generator. I'm assuming devices connected to a 12v battery won't really like 19v!

[thm_w]

If they battery is jumping from 14V to 19V like that its dead. Internal impedance is very high.

The noco is probably using some probing to determine if its connected to a decent battery that will take a charge. Will be some info in the manual.
It should show an error LED after it detects the bad battery and won't try to charge it.

It would be good if you had a battery tester, as some batteries will still take charge, but will be almost dead/almost useless.

[SpookyGhost]

Thanks, good info. The batteries its doing it on are the very oldest ones, so that makes sense

Do you think 19v could cause an issue to 12v electronics?

Sadly zilch in the book about it spiking up

[thm_w]

Thanks, good info. The batteries its doing it on are the very oldest ones, so that makes sense

Do you think 19v could cause an issue to 12v electronics?

Sadly zilch in the book about it spiking up

Any circuit designed to run from automotive 12V would not have an issue.
However, if you are using a custom power supply or your own design, then you need to check if it can handle these higher voltages.

There is some mention of high voltage here: https://no.co/support/sulfation-and-battery-repair-mode but I dont think that applies to your charger.

[BrokenYugo]

It is almost certainly designed to do that, very dead lead acid batteries will sometimes come back and start taking a charge (typically with permanently degraded performance) if higher voltage is applied at first. As mentioned by others in thread, the battery and anything properly designed for automotive use won't mind it, but if a battery is that far gone it probably won't be useful anyway.

[SpookyGhost]

Thanks guys, very good information

I'm going to toss those batteries. So far a good few of them seem alright.

Now to think of a project for old 12v SLA batteries...