Always wear eye protection and protective clothing when working around lead-acid batteries!
The most Amp-Hours for dollar and longest life are found in industrial lead-acid wet cells. Electrical energy is stored by chemical reaction. Proper care does not require "babying" the batteries - they are made for repeated deep cycling. Long life is based on proper charging and periodic maintenance.
3-stage charging refers to an automatic reducing of the charge voltage and current as the battery approaches full. The stages are referred to as Bulk, Acceptance, and Float. Both PV controllers and AC chargers should use this sequence. Smaller systems can use a 2 stage process and really small systems may just shut off the charge at a certain voltage.
The ideal set-points for charging vary with temperature and chargers may include a temperature compensation probe to automatically adjust for this. Often this is an option that should be purchased if the temperature of the batteries varies.
Once a system is set up the regulation of charging is automatic with the exception of equalization - an occasional overcharge which stirs the electrolyte and brings any undercharged cells up to the proper level. A voltmeter can be used to check each battery to see if this is necessary. Typically this should be done after a number of exceptionally deep cycles or every 1-3 months. Again, this is a feature you should look for in any charger. Trace and OutBack inverter/chargers and charge controllers all include this feature, as do the Blue Sky Energy charge controllers.
Wet cells also periodically need distilled water added to replace what bubbles off during bulk charging. I like to add water just before equalizing to assure good mixing. New batteries may go six months without needing water and as they age require it more frequently. Do not overfill! This dilutes the electrolyte. They should be filled only to about 1/8" to 1/4" below the BOTTOM of the tube under the filler cap.
All connections should be periodically checked for tightness and oxidation. Once oxidation sets in some sort of grease is necessary to keep it in check. It is easy to periodically check each battery's standing voltage. Wide descrepencies may indicate a poor connection or a system design problem. Small descrepencies are almost unavoidable with multiple batteries. It is not unheard of to occassionally rearrange batteries to compensate for this.
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