Xantrex Technology 10 - Manual (Page 48)

Operation
3–10 975-0251-01-01
Parallel
Connecting two batteries in parallel will double the amp hour rating of the
battery bank, while the voltage will be the same as each individual battery.
For example, two 12 volt 105 amp-hour batteries in parallel will produce one
12-volt, 210 amp-hour battery bank.
Only similar batteries should be connected together in one bank. Do not
connect old and new batteries or wet and gel cell batteries together. In the above
drawing, note that the load is connected to the positive terminal of the first battery
and the negative terminal of the last battery. This practice helps to balance the
battery bank.
Battery Bank Ratings and Sizing
Deep-cycle batteries are usually rated in amp hours. The amp-hour rating is
based on a 20-hour discharge cycle; therefore, a 100 amp-hour battery can deliver
5 amps for 20 hours. If the discharge rate is greater than 5 amps, the available amp
hours are decreased. If the load is increased to 100 amps, only about 45 amp hours
will be available.
Another common rating is reserve capacity expressed in minutes. This is derived
by placing a 25 amp load on the battery and measuring the time until the battery
voltage reaches 10.5 volts.
Deep-cycle batteries can be discharged about 80% before permanent damage
occurs, though shallower cycling will result in much longer battery life. Fifty per
cent cycling is generally considered to be a good compromise between long
battery life and a reasonably sized battery bank.
To achieve 50% cycling, you should calculate your amp-hour consumption
between charging cycles and use a battery bank with twice that capacity.**
Figure 3-6 Parallel Battery Connection
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Important: Always use proper terminals for your interconnecting battery cables and
cable which is 2 AWG or larger.