Wet Lead Acid batteries are the most common batteries
used in energy systems because of their price, local availability,
and ease of recycling. A properly maintained lead acid cell will last about
ten years. This type of battery will deliver about 1000 full charge-discharge
cycles. The drawbacks of Wet Lead Acid Batteries include the following:

• They need to be equalized about every month
• The water needs to be replenished
  often
• The batteries corrode — contacts need to be cleaned frequently
• The
  batteries are not freeze-tolerant and they need to be in a warm environment
  or need to be insulated
• The batteries release gases while charging so
  they need to have an exhaust vent leading outside

Good Brand of Lead Acid: Surret or Trojan

Gel Cell batteries are also lead acid but the electrolyte
is in gelatin form instead of liquid. Thus, they need no maintenance — water
does not need to be added, and it doesn’t corrode. They can also be stored
in any position and since there are no dangerous fumes, they can be placed
in any part of the house. It will not freeze (when fully charged, it can
function in -30C or -20F). These batteries are ideal for part-time dwellings
where they can be left unattended for long periods of time. Its drawbacks
include the following:

• Delivers only about 200-500 full charge-discharge
  cycles
• Three times more expensive than wet lead acid batteries
• Even in a well-maintained
  system, life expectancy is shorter than that of wet lead acid batteries

Good Brand of Gel Cell: Universal Battery

AGM
is a newer
type of sealed battery uses "Absorbed Glass Mats", or AGM between
the plates. This is a very fine fiber Boron-Silicate glass mat. These
type of batteries have all the advantages of gelled, but can take much
more abuse.

AGM
batteries have several advantages over both gelled and wet (flooded)
batteries. Since
all the electrolyte (acid) is contained in the glass mats, they cannot
spill, even if broken. This also means that since they are non-hazardous,
the shipping costs are lower. In addition, since there is no liquid to
freeze and expand, they are practically immune from freezing damage.

Nearly
all AGM batteries are "recombinant" — meaning that the
oxygen and hydrogen recombine inside the battery. These use gas phase
transfer of oxygen to the negative plates to recombine them back into
water while charging and prevent the loss of water through electrolysis.
The recombining is typically 99+% efficient, so almost no water is lost.

The
charging voltages are the same as for any standard battery — no
need for any special adjustments or problems with incompatible chargers
or charge controls. And, since the internal resistance is extremely low,
there is almost no heating of the battery even under heavy charge and
discharge currents. The Concorde (and most AGM) batteries have no charge
or discharge current limits.

AGMs
have a very low self-discharge — from 1% to 3% per month is usual. This
means that they can sit in storage for much longer periods without charging
than standard batteries. The Concorde batteries can be almost fully recharged
(95% or better) even after 30 days of being totally discharged.

AGMs
do not have any liquid to spill, and even under severe overcharge conditions
hydrogen emission is far below the 4% max specified for aircraft and
enclosed spaces. The plates in AGM’s are tightly packed and rigidly mounted,
and will withstand shock and vibration better than any standard battery.

Even
with all the advantages listed above, there is still a place for the
standard flooded deep cycle battery. AGMs will cost 2 to 3 times as
much as flooded batteries of the same capacity. In many installations,
where the batteries are set in an area where you don’t have to worry
about fumes or leakage, a standard or industrial deep cycle is a better
economic choice. AGM batteries main advantages are no maintenance, completely
sealed against fumes, hydrogen, or leakage, non-spilling even if they
are broken, and can survive most freezes.

Good
Brands of AGM Batteries: Universal
Battery or Concorde.