View Full Version : Help me restore this old deep cycle battery

Tan Lam
5th August 2007, 14:05

I found a deep cycle battery and I would like to try to restore it. I have applied 14.5volts for 48 hours to try to charge the battery, but even after 48 hours the open circuit voltage is only at about 12.36 volts. After charging, I did a specific gravity test with a hydrometer, and the specific gravity is very very low. So I was wondering if it would still be possible to restore this battery. What does such a low specific gravity mean? Does it mean the electrolyte is almost all water? I took off the caps on the top of the battery and the electrolyte is already full to the top. If so, I was thinking maybe to just empty out all the old electrolyte, fill it with new battery acid + EDTA dissolved in water to desulfate the plates. What do you guys think? Will this work?

Paul Bailey
5th August 2007, 17:34
There are probaby lots of users in the group that have ended up with Used batteries at some point. And the truth in almost all cases is that there is a definate reason why they are being sold in the Used market so don't spent too much time and effort hours on this.,and money as well.. Good batteries cost lots of $$$$$ for a reason. , Lots of mixed reviews with EDTA and Desulphators. Either way the capacity may never be the same if you have Mild success with whatever for of Trick to restore it.. . Not meaning to sound harsh BUT there are a few sayings that hold true here. 1) People Kill most batteries thru neglect / or improper maintenance . An old battery is still old no matter what Miracle you pull off to try and FIX it. . 2) Don't buy an old battery in the first place unless you are seeking the experiance and want to play Fix it.. More to follow as I'm sure others will have lots to say about this.. Paul:)

Tan Lam
5th August 2007, 17:48
You are making it sound like I actually BOUGHT this battery. I actually found it laying around in a gas station and the attendant let me take it =)

Joe Blake
5th August 2007, 20:48
Dr Frankenstein used electricity to bring his creation to life, but generally speaking once a battery is dead it pretty well stays dead. At present, the market for lead-acid batteries is pretty much slanted towards new ones, but if things continue on their present trend, and the number of hybrid/electric vehicles continues to increase, then old batteries may become more valuable as a source of recycled materials to build new ones, so perhaps keep hold of the battery until then. My experience is unless you KNOW how the battery has been treated in the past, don't spend too much time or money on trying to restore it to life. De-sulphation works, occasionally, but not often.


Paul Bailey
5th August 2007, 21:27
Hi Tan : welcome to the Group... Kind of a bad start with a hard reply reply to a new member. . Oooops! A free battery is great and allows you to try all the available Tricks out there for rejuivination. , which may or May not work for you. Experience says its possible for some short term gain but won't last unless the battery has endured only minor neglect and it may come back 100% . I'm all ears for cures, Even guys with 30 years battery experiance just don't know it all, and as stated by Joe : you would have to really know how the battery has been treated in the past.. Now what may work is a constant charge current for at least a couple weeks. (current amount is fixed and based on the Ahr rating of your Battery). I'm sure others will comment ,. Fire away and enjoy the weekend Paul:)

Tan Lam
5th August 2007, 21:41
Thanks for the replies everyone. Of course I would love to be able to rejuvenate this battery to a usable state, but a good learning experience would be nice too. I consider this battery a "guinea pig battery" so I probably wont mind doing some strange and extreme thing to try and get it working (if anyone has any suggestions, feel free to tell).

I actually built two chargers a while back. I initially charged this battery with about 1 amp at 13.8 volts, but the voltage only climbed to 12.36v. I am now hooking it up to my other charger (which I built from 3 atx power supplies hooked in series) and it is applying about 14.9 volts to the battery. I am going to leave it charging until tomorrow. Currently the open circuit voltage is about 12.7 volts, but I didnt let it sit for a while. Its pretty hard finding a cheap source of EDTA, so I think I am just going to try to drain out all the acid, fill it up with filtered water from my fridge, connect it to my 14.9 volt charger for a few days to maybe loosen up the sulfation, then readd the old acid.

Mark Parsons
20th August 2007, 13:27
Greetings Tan,

If you feel qualified to play around with 120VAC I would love to hear a report on whether this simple circuit can restore your old dead battery.