The Optimate Pro-S is a battery charger/de-sulfator, made by Tecmate. The model I purchased came from www.batteryxpress.com and is the older version. The difference between the 2 is in the styling and the new model lets you choose the type of battery connected to it.
I purchased this battery charger because I have a growing collection of sealed lead acid batteries removed from uninterruptable power supplies. Many of them are completely dead but some may be just sulfated.
The unit claims to be able to recover a battery with as low a voltage as .8. It is primarily designed for "power sport" Lead acid batteries, used in ATV's, and motorcycles, but will work on any 12 volt lead acid battery.
Once I received the unit I selected some batteries, including one that had .5 volts. I expected the one with only .5 volts to fail but would try it anyways. As expected the .5 volt battery did not even register with the charger. I attached the battery to a standard charger which did not see it either. So I tricked the regular charger by jumpering a good battery to the bad battery while it was on the charger. This started it charging. Once it got to about five volts I hooked it to the Optimate. Interestingly enough it did not do a desulfate which is strange for a battery of this age (I later found out why). I left it on the charger for 24 hours but it was a no go.
I decided to just try batteries with at least 12 volts. It took a call to the manufacturer and some experimenting, as the instructions are written kind of like a run on sentence in a computer program. Here is what I found. If the charger is turned on when connected to the battery (manual says to do this) it does not check if the battery is sulfated even though the manual says that is the first thing it will do, however if the charger is connected to the battery after it is turned on it will test for sulfation. It appears that this is a bug in it's programming. The newer unit is supposed to be better behaved. The unit is supposed to indicate if a battery is good, ok, or bad using 3 lights, Green, Yellow, and Red. With combinations of the Green and yellow light for readings in between good and ok. I was never getting an indication of whether the batteries were any good. Just to test I hooked it to a known good battery and left it overnight. In the morning it registered good. So I started trying other batteries. I quickly found 2 other batteries that were good and I didn't know it.
I also found that If you repeatedly desulfate a battery you can revive it. Case in point I have 5 batteries that would not register as good, bad, or in between. I found that if I cycle though the batteries, letting each battery rest after its desulfating cycle, over time the resting voltage slowly climbs up. This worked so well that a battery I found that had a date code of July 1996 was brought back to good condition. Only testing will tell if it really is good, but the results were surprising.
I have also ran it on several of my car batteries, to see if they are still good, and they all are. I probably should have paid extra for the newer version, but once I got the kinks worked out, I am quite happy with the unit.
Update 5-6-10 None of the sealed lead acid batteries I tested, were revived enough to be used in a ups again. They could be used for other purposes but the UPS's would reject them.
Update 6-24-2012 From further research and testing it appears that the claim of reviving totally dead batteries is not possible. As my experiments showed.