This is from an article in Auto Restorer magazine, April, 2014, on keeping your WalMart battery going, and going, and going.
The wire line telephone industry has depended on lead-acid batteries for more than 100 years. These battery strings are well maintained, kept on a constant float voltage, and the batteries last for decades.
You can't expect auto batteries to last decades, but keeping a float charge will definitely extend life. Solid-state battery maintainers (Google battery tender jr, under $25) do supply a small float charge, but even some of the best units might overcharge. Over long periods, they can evaporate the elecrolyte or break down the water to oxygen and hydrogen.
A better and safer way is to use a battery maintainer or charger on a household timer for only about an hour or two per day. This applies to a car with no computer, with no constant normal battery drain.
If using a battery charger, not a maintainer, connect a 'ballast lamp', an instrument panel bulb, in series with one of the charger leads, to lower the current.
Using a charger with balast lamp one or two hours per day should prevent over-voltage, boil off, and electrolysis. Check the voltage occasionally, and adjust the timer as needed. Battery retailers used to keep one charger connected to dozens of batteries with one ballast lamp per battery.
To preserve elecrical connections from moisture, acid penetration, and formation of oxides, use a conductive grease such as No-Oxide A. You can buy a 2oz tube, a lifetime supply, from telephonetools.com.
