A friend ask me the other day why car batteries don't need to have water added anymore.
Anybody know?

 

They are different types of lead acid batteries that allow for less maintenance, one is absorbed glass mat where there are pads basically that hold the acid in solution, another type has a vent system that allows gasses to escape but minimal amounts evaporate due to its construction, both types usually have hidden ports so they can be serviced however may not require adding water throughout their life especially if not overcharged

 

Around here this year, there is enough rain it just keeps the battery topped off.

But if your friend was talking about a standard not AGM battery the manufactures years ago, (1970s?) figured out that people didn't ever check the level in the cells. So they added more electrolyte when making them to take care of the problem, and sealed them with plugs that have over pressure vents.

 

... The former battery design, with removable cell covers, had one dangerous flaw. Under certain conditions, the \(H_2O\) in the battery could be separated by a charging current into its elemental parts, \(H_2\) and \(O_2\), which would combine again, explosively, given any small spark. ... Not a. good idea, since sulphuric battery acid was also part of the resulting spray. ... I can attest to that personally. ... Probably one of the reasons that protective eyewear is now required in many workplaces such as service garages.

 

I believe they found that alloying calcium with the lead reduces the outgassing of the water into hydrogen and oxygen, thus eliminating the need to periodically add water.

 

I believe they found that alloying calcium with the lead reduces the outgassing of the water into hydrogen and oxygen, thus eliminating the need to periodically add water.

Exactly. The early 70's is when I worked in the battery industry for a bit. The older style lead acid batteries used a Lead-Antimony alloy for the plate grids. The 'newer' low maintenance batteries use a Lead-Calcium alloy to make the grids. Lead-Calcium has a significantly higher gassing potential than does Lead-Antimony.

 

In addition to the improvements described, modern charging systems have less tendency to cook the battery, plus the warranty is much shorter and so they don't go dry until they fail anyway