Electrical system
81
Two batteries connected in series retain the capacity
but double the voltage. During charging, each battery
receives the current supplied by the charger. The total
battery voltage must not exceed the battery voltage
marked on the charger.
When connecting two 12 V batteries in series and one
battery has a short-circuited cell, the resting voltage
across the two batteries will be approx. 23 V.
Parallel connection:
Two (or more) 12V batteries are connected in parallel
so that the capacity is increased. The boat’s system
voltage is the same as the battery’s rated voltage.
• The batteries must have the same nominal volt-
age.
• The batteries may have different capacities.
• The batteries need not be the same age.
When two batteries are connected in parallel, the volt-
age remains the same but the capacity is the sum of
all the capacities. When charging, each battery re-
ceives a charge lower than that stated on the charger.
To find out the charge current supplied to each bat-
tery, measure the charging current to each battery
with an amperemeter.
If one of two batteries connected in parallel has a
short-circuited cell, the nominal system voltage will be
approx. 10 V.
12V
70Ah
12V
70Ah
12V
140Ah
Example: When two 12 V batteries each with a capacity of 70 Ah
are connected in parallel, the voltage will be 12 V and the total ca-
pacity 140 Ah.
Example: When series connecting two 12 V batteries with a ca-
pacity of 70 Ah, the voltage is 24 V and the capacity 70 Ah.
12V
70Ah
12V
70Ah
24V
70Ah
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