I'm trying to charge a riding lawn mower battery with a 12 volt, 10 amp/ 2 amp charger. I'm told I should have it on the 2 amp setting for this. Before charging, the battery tested at less than 1 volt. After charging 14 hours, it shows 3.5 v. Checking output of the charger, I get 4.5 volts. The test/charging indicator needle does not move. What's up? Is it operating properly or not, and why? Thanks! I do some household electrical repairs, but I'm not familiar with DC or electronics at all.

 

I'm sorry to say that that battery is useless. It sounds like you have one good cell left, but by putting that charger on it, you will end up killing it too.

So, here is how you fix things. Find out where you can safely re-cycle or dispose of the battery, then take it there. Then go and buy a new one, charge it with your charger according to the battery manufacturers recommendations and you'll be in business.

If a 12V lead acid battery falls below about 7.2V for any appreciable length of time (days or weeks at the most), it will likely be unrecoverable. If it falls to less than 1 volt I would bet my last dollar that it is just hazardous waste. Time to buy an new one.

Sorry .

 

I really appreciate the reply, even though it's "bad" news about the battery. But what about the charger only putting out 4.5 Volts? Is it bad too? Thanks again.

 

Is that without any load on it?

 

Yes, just attaching test leads from a dmm to the charger's spring clamps.

 

It may still be okay. Many low priced chargers use what is called half wave rectification. A lot of meters will measure such a signal as somewhat less than V(peak)/pi. If this is the case, then you are alright.

Do you have an electrolytic capacitor at your disposal? Something with a 25V operating voltage and about 100uF or more would be ideal. Just attach to the leads of the charger (observe polarity, this is important!!!) and make the measurement again using your DMM.

An alternative would be to put the charger on a good battery. Measure the voltage of the battery before you put the charger on it and a few minutes after. The voltage should increase.

 

OK--thanks again very much! I'll check the charger on the new battery when I get it. I don't have a capacitor, and I'll have to go further in the e-book tutorial to begin to understand the rest of your answer more fully! I look forward to that.

 

I'm trying to charge a riding lawn mower battery with a 12 volt, 10 amp/ 2 amp charger. I'm told I should have it on the 2 amp setting for this. Before charging, the battery tested at less than 1 volt. After charging 14 hours, it shows 3.5 v. Checking output of the charger, I get 4.5 volts. The test/charging indicator needle does not move. What's up? Is it operating properly or not, and why? Thanks! I do some household electrical repairs, but I'm not familiar with DC or electronics at all.

I would look into a replacement battery charger or repair that one. I accidentally reversed the leads on my 12-volt charger hooked to a 12-volt battery and something not good happened. Checking the voltage on the output leads showed me 4.5 volts. I checked the output of a similar 6-volt charger and it showed 6.15 volts. I then opened the 12-volt charger and I see two diodes, and one of them is blown open (I can see the insides of the diode). I think it cannot charge 12 volts if it is outputting 4.5 volts (and is probably dangerous to continue to be used in that condition). Roll Tide!

 

I would look into a replacement battery charger or repair that one.

You do realize this thread ended more than 12 years ago. I think the OP may have come upon a solution by now.

 

You do realize this thread ended more than 12 years ago. I think the OP may have come upon a solution by now.

Maybe someone is looking for information, like I was today, and any additional info may help that person with his/her issue.

 

I suggest trying the charger on the higher current setting for just a few minutes, and then checking the voltage after disconnecting the charger. My experience with lead/acid batteries has been different. If the battery is truly worn out, that is one thing. But some times they need a harder push, but only for a few minutes, 5 to 10 at the longest.

 

Maybe someone is looking for information, like I was today, and any additional info may help that person with his/her issue.

Fair enough.