SPECIFYING BATTERIES, CHARGERS
& ALTERNATORS
The inverter will require Deep
Cycle Lead Acid Batteries
of appropriate capacity.
Lead-acid batteries can be categorized by the type of application: automotive service -
S
tarting/
L
ighting/
I
gnition (
SLI
, a.k.a. cranking) and
deep cycle
service
SLI Batteries
Everybody is familiar with the SLI batteries that are used for automotive starting and
powering vehicular accessories. SLI batteries are designed to produce high power in short
bursts but must be constantly recharged (normally with an alternator while driving).
Vehicle starting typically discharges 1%-3% of a healthy SLI battery’s capacity.
The automotive SLI battery is not designed for repeated deep discharge where up to 80 %
of the battery capacity is discharged and then recharged. If an SLI battery is used for this
type of application, its useful service life will be drastically reduced
Deep Cycle Batteries
Deep cycle batteries are designed with thick-plate electrodes to serve as primary power
sources, to have a constant discharge rate, to have the capability to be deeply discharged
up to 80 % capacity and to repeatedly accept recharging. They are marketed for use in
recreation vehicles (RV), boats and electric golf carts – so they may be referred to as RV
batteries, marine batteries or golf cart batteries. There are two categories of deep cycle
lead acid batteries – wet and sealed. A wet cell battery has a high tolerance to overcharg-
ing. However, it will release hydrogen gas when charging that must be properly vented
and the water level must be checked frequently. Sealed batteries can either be Gel Cell or
AGM (
A
bsorbed
G
lass
M
at). Both the Gel Cell and AGM are maintenance free, have no
liquid to spill and gassing is minimal. The Gel Cell is the least affected by temperature
extremes, storage at low state of charge and has a low rate of self discharge. An AGM
battery will handle overcharging slightly better than the Gel Cell
Units of Battery capacity
The battery capacity is the measure of the energy the battery can store and deliver to a
load. It is determined by how much current any given battery can deliver over a stipulated
period of time. The energy rating is expressed in
A
mpere
H
ours (AH). As a bench mark,
the battery industry rates batteries at 20 hour rate i.e. how many Amperes of current the
battery can deliver for 20 hours at 80 º F till the voltage drops to 10.5 Volts for 12 V
battery and 21 V for 24 V battery. For example, a 100 AH battery will deliver 5 Amperes
for 20 hours. Battery capacity is also expressed as
Reserve Capacity (RC)
in minutes.
Reserve capacity is the time in minutes for which the battery can deliver 25 Amperes at
80 º F till the voltage drops to 10.5 Volts for 12 V battery and 21 V for 24 V battery.
Approximate relationship between the two units is as follows:
Capacity in AH = Reserve Capacity in RC minutes x 0.6
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