The only way that I know of which will provide deep cycle lead-acid batteries for 20+
years is to store away enough so that when a battery "wears out" (and it will), it can be
replaced. Car batteries can be used for a short while until a community collects and
prepares enough deep-cycle batteries. There are a few things to keep in mind. A
discharged battery, left in that state for more than a couple or three months looses a great
percentage of it full charge capacity. It is therefore most important to collect batteries as
a priority activity pre pole shift and/or post pole shift. For the long run, and for storage
for a latter time, forget auto batteries or even heavy duty heavy equipment "starting"
batteries. They are designed to provide lots of current for a short time and do not hold up
to deep discharge. Collect "deep cycle" marine type batteries, and batteries found in
cellular phone relay stations.
The first thing one should do with a salvaged battery is to fully charge it by whatever means possible. Once fully changed (use a hydrometer battery tester, very inexpensive), completely drain the battery acid and store in tightly closed glass containers in a dark place. Rinse out the battery with distilled water and store any place out of the way. It may not be put into service for many years. When separated, the battery acid (sulfuric acid) and the empty battery will keep indefinitely. To place it into service, simply replace the stored battery acid. It would be a good idea to stock several gallons of concentrated sulfuric acid. This will prolong the life of aging batteries.
When charging batteries, do not charge at a rate of over 40 amps, and 20 amps is even better. A very high charge rate can deform the lead plates causing shorts and open's between cells within the battery. This is why you need a "bank" of batteries to charge in parallel if you have a high current output generator. An 80 amp output from a generator should be connected to 4 12 volt batteries connected in parallel. This will provide a charging current to each individual battery of 20 amps, a safe level.
Understand the battery rating level for the battery. I have an 850 amp-hour deep cycle battery that I keep trickle-charged for emergency Ham Radio communications. The 850 amp-hour rating means that the battery can theoretically provide a maximum of 850 amps at 12 Vdc for one hour. In reality, it cannot provide this amount of current because of internal resistance. It can, however, provide 850 hours of 12 Vdc at one amp, or 85 hours at 10 amps, or 42.5 hours at 20 amps, etc.
The last thing. Keep careful watch on the battery fluid level on all batteries "in service".
Add distilled water as the fluid level drops due to electrolysis.
Offered by Ron.