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OK, most of you know how much of a fanatic I am with my wagon, and most cars in general. I do 99% of my own work and do more than I need to keep my cars running strong. Sunday I noticed a problem and started looking for the culprit..... ;) Heres the way it went down.

We have had alot of very hot weather here this summer in Northern Ohio and Saturday was another 95+ day, no problems. Since I installed my gauges I have been able to keep and eye on my trans temp and my electrical system voltage. The voltage runs between 14.0 and 14.2 all the time. I had 2 hours of highway driving in the heat of the afternoon on Saturday.

Sunday back on the highway, I noticed my voltage in the 70+ deg cooler morning was running around 13.8 to 13.7 at speed and would drop to 13.5 / 13.4 at a stop light. When I got to the show I opened the hood for a look and poped the caps off my battery to start. Well, problem solved. My 4 year old battery (maint free BTW) was low on water, about .75 litre when it was filled. On the way home, it worked its way back up to 14.0 and today it was back to normal 14.0 / 14.2 volts.

I am sure that most people today dont check their batteries, but I have now put that up on my check list of regular things to do.
 

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When I got to the show I opened the hood for a look and poped the caps off my battery to start. Well, problem solved. My 4 year old battery (maint free BTW) was low on water, about .75 litre when it was filled. On the way home, it worked its way back up to 14.0 and today it was back to normal 14.0 / 14.2 volts.

I am sure that most people today dont check their batteries, but I have now put that up on my check list of regular things to do.
I'd just like to add that it's a common misconception that you need to "add" water to the battery if its low. Which is totally incorrect. For one, inside the lead-acid battery is a solution of sulfuric acid and water not just water. For two what your essentially doing is diluting the electrolyte content of the battery, making it weaker than it was in the first place. Maintenance-Free means your not supposed to crack open the caps to "check" or "top off" the fluid levels. Many manufactures have a "do not open" warning lable on the top some where. But even if the caps look like they where meant to be open , they are often glued down. Also Hydrogen gas is a normal byproduct of lead-acid battery charging. Opening the caps . again only degrade battery life. Maintenance-Accessible or "Low Water Loss" batteries are a whole other story. Distilled water yes, Tap water no.
 

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Assuming you dont have a leak somewhere, in which you would need to add "battery acid" back into your cells. That is around 34% sulphuric acid.

Yes, even on "maintenance free" batteries, you do need to maintain them. They are just usually maintenence free for the warranty period. Overcharging or depletion of a battery can cause water boil off as water boils off at 212F and sulphuric acid boils at 639F.

If your batteries got hot enough to boil off the sulphuric acid in a maintenance free battery, it would probably warp the plastic. The caps are vent caps because hydrogen gas is a normal by product of battery charging. If they are totally sealed the inside of the battery would get pressurized and "forcefully" vent its contents.

If you're that concerned about the concentration of acid in your batteries and want to know if you should add acid or water, spend the $5 on a battery hydrometer... you know, the little medicine dropper looking thing with the floating balls inside of it? They make them for coolant too.
 

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You did the right thing by adding water. I hope it was distilled water though, because the minerals in tap water can reduce the capacity of the battery. If it was tap water, I wouldn't worry about it too much (tap water is better than no water and an alternator failure). You might not even notice a difference.

If the battery is overcharged (bad regulator) or low on water, the battery will heat up and release water vapor, oxygen, and hydrogen gas (from splitting of water molecules). This is where your battery water went unless you had a loose cap or something. Since the acid doesn't really evaporate (unless your battery is on fire), it gets more concentrated, the top of the plates are no longer submerged, and the internal resistance goes way up. The battery gets even hotter while the alternator is straining to push current though it in vain, and the water loss accelerates. One or the other will give up eventually, so it's good you caught this.

To restore the battery, you just add back the water that was split or evaporated, and the specific gravity of the electrolyte should be right back where it started (minus any plate sulfation). If you add acid instead, you will end up with an overly high specific gravity since the cell has more acid than when it was new.

If the battery will not charge and has vent caps, the first thing I check is the water levels, even on maintenance free batteries. All six cells should be filled with distilled water until they touch the bottom of the plastic sleeve. It can make a big difference. Unless the battery was stored in extreme conditions (like a hot desert climate) or subjected to chronic overcharging, you shouldn't have to mess with the water levels if the battery is newer than 2-3 years, hence the "mostly" maintenance free part. Sealed gel (Optima) and AGM batteries are another matter (they don't have vent caps so you can't do anything, nor should you).

Like skrenos recommended, you can buy a cheap battery hydrometer and test your cells. But if the specific gravity is low in a few cells, you still shouldn't add acid because it means you have some other problem that has tied up the acid (undercharged cell, sulfation, or stratification). If you add acid, you will compromise the capacity of that cell, and it will charge and discharge at different rates compared rest of the cells. This focuses all the wear and tear on that cell, so your battery will die faster (it only takes one bad cell). So the hydrometer is more of a diagnosis tool rather than an adjustment tool. The only time you add new acid to a battery is after you've drained the old acid and done a few rinse/charge cycles with distilled water to remove any remaining lead sulfate on the plates. If the battery is sulfated from sitting discharged this might work, but if the plates are warped, shorted, or deteriorated from normal use or overcharging, it might only buy you a few months until you need a new battery.

Trivia: WWII subs carried large banks of lead acid batteries to power their electric motors when submerged. All the charging/discharging cycles caused water loss in the same fashion as discussed above, so the battery technicians would constantly be topping off the batteries with fresh water. Because the batteries were so big (about 100 tons worth per sub!), this amounted to a fairly substantial water use on the sub (perhaps 500 gallons per week). As a result, about 20% of the sub's fresh water supply was strictly for battery use! How would you like it if you couldn't take a shower for weeks just to keep your batteries topped off? :ugh:

Sorry for writing an encyclopedia article but hopefully someone will find it helpful… :gives:
 

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behlinla is right, add water not acid. The charging process restores water to its electrolytic (1/3 acid) state.
 

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I've got a Battery Minder w/conditioner that desulfates the battery.
I brought my SeaDoo battery back with it for another season. Got the SeaDoo used so I don't know how the battery was stored but by getting another season out of it the Battery Minder paid for itself.
I now rotate the conditioner among the stored vehicles that already are on float chargers.
 
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