What is the difference between battery repair fluid and distilled water?

[JeremiahFitz]

The difference between the two lies in their composition. The sulfuric acid concentration in repair fluid is lower than that in the original electrolyte or replenishment fluid. Distilled water is pure water that does not contain any mineral elements or impurities. Below are the relevant introductions: 1. Battery repair fluid: Battery repair fluid, also known as lead-acid battery repair fluid, battery activator, or battery capacity enhancer, can restore the capacity of failed batteries, extend their service life, and improve various battery performances when added to them. 2. Distilled water: Distilled water refers to water that has undergone distillation and condensation processes. Water distilled twice is called double-distilled water, and water distilled three times is called triple-distilled water. It is low-oxygen-consuming water, often treated with potassium permanganate and acid. Industrial distilled water is obtained through distillation methods.

[StWalker]

I had researched this when tinkering with old car batteries. Distilled water is just regular pure water, specifically used to replenish the evaporated water in the battery, as the liquid level drops over time with battery usage. However, battery reconditioning fluid is different—it contains sulfuric acid or special additives, mainly to address sulfation on the plates. If an old battery won’t hold a charge or has unstable voltage, sulfation might be the issue. But I must warn you: never casually add reconditioning fluid! Using the wrong concentration or type can actually damage the battery. My neighbor ruined his battery by adding the wrong stuff. If it’s just regular water loss, the safest approach is to take it to an auto repair shop to test the electrolyte density before deciding whether to add distilled water or electrolyte. Nowadays, many new batteries are maintenance-free and don’t require water refills.

[XavierRose]

I think the difference is quite obvious in terms of composition. Distilled water is just H₂O, completely free of impurities, and its only purpose is to replenish the missing water in the electrolyte. On the other hand, battery restoration fluid has a much more complex composition, containing specific chemicals like potassium salts and sulfuric acid, mainly aimed at addressing issues like internal crystallization in the battery. But honestly, the effectiveness of restoration fluids is quite questionable. I've tried several products that claim to 'revive old batteries,' and none of them had lasting effects. What really works is regularly checking the fluid level and topping it up to the mark with distilled water. Also, a quick tip: if the battery terminals are white and corroded, pouring hot water over them is more effective than adding any restoration fluid.

[Aaron]

Here's a tip I learned from an auto repair master: Distilled water only replenishes lost moisture without altering the electrolyte concentration. Repair fluids, on the other hand, are chemical solutions like desulfators designed to dissolve crystalline deposits on plates. But here's the catch – it's hard for non-professionals to determine whether a battery is dehydrated or internally damaged. I learned this the hard way when I added repair fluid to a weak battery, only to disrupt the concentration balance and render it unable to charge. Later, I bought a $10 hydrometer to first measure the electrolyte specific gravity: below 1.28 means you should replenish with electrolyte, not water; above 1.28 indicates dehydration where distilled water should be added. Repair fluid is only recommended for old batteries confirmed to have sulfation that can still be salvaged.