Also check the condition of the battery cables. Should you need new ones, here's the latest information about cable sizing. Your boat sits in the water/on a lift most of the time correct? If so that's a harsher environment on your electrical system so look everything over carefully the best you can including the cable end connectors on/behind the battery switch.
Mercruiser Service Bulletin No. 2002-12
New Battery Cable Gauge Recommendation Information.
This new battery cable recommendation will be going into the service manuals and installation manuals.
NOTE:
Battery should be located as close to engine as possible.
Step 1. Select proper size positive (+) and negative (-) battery cables using the chart. Step 2. Add the positive and negative cable lengths together. Step 3. Divide by 2 to obtain the average cable length.
IMPORTANT: Terminals must be soldered to cable ends to ensure goodelectrical contact. Use electrical grade (resin flux) solder only. Do NOT useacid flux solder, as it may cause corrosion and a subsequent failure.
Cable Length, Cable Gauge
Up to 1.1 m (3â1/2 ft.) 25 mm2 (4)
1.1â1.8 m (3â1/2 â 6 ft.) 35 mm2 (2)
1.8â2.3 m (6 â 7â1/2 ft.) 50 mm2 (1)
2.3â2.9 m (7â1/2 â 9â1/2 ft.) 50 mm2 (0)
2.9â3.7 m (9â1/2 â 12 ft.) 70 mm2 (00)
3.7â4.6 m (12 â 15 ft.) 95 mm2 (000)
4.6â5.8 m (15 â 19 ft.) 120 mm2 (0000)
With the old battery cable recommendation, the negative (-) and the positive (+) battery cables were measured separately. Then you selected the correct cable gauge to fit the length measured for each. This was OK if they were both the same length. It did not work well if there was a battery switch installed in the positive (+) battery cable, between the engine and battery. Then, the positive (+) cable had to use a much larger gauge than the negative (-) did.
In the example below, this would have meant the shorter 91.4 cm (36 in.) length negative (-) cable would have used a 25 mm2 (4) gauge cable. The longer 579.1 cm (228 in.) positive (+) cable would have used 120 mm2 (0000) gauge.
Example:
A person measures 91.4 cm (36 in.) length of negative (-) cable between engine and battery. They measure 274.3 cm (108 in.) of positive (+) cable between the engine and the battery switch and 304.8 cm (120 in.) between the battery switch and battery. Add 91.4 cm (36 in.) + 274.3 cm (108 in.) + 304.8 cm (120 in.) = 670.5 cm (264 in.) divide by 2 = 335.3 cm (132 in.) or 3.4 m (11 ft.). So BOTH the negative (-) AND positive (+) battery cable use the 70 mm2 (00) gauge cable.By using the same gauge battery cable, 70 mm2 (00) gauge in the example above, for BOTH the negative (-) and positive (+) cable, the longer length positive (+) cable can use a smaller gauge cable than it would have if the negative (-) and positive (+) gauges were sized to their respective lengths. New Minimum EFI and MPI Cranking Battery Requirements
Models Affected
All EFI (TBI) and MPI models, including all product produced prior to this service bulletin.
NOTE:
All EFI and MPI products produced prior to this bulletin have to meet this newrequirement when the current battery in the boat has to be replaced.
NOTE:
Carbureted engine minimum battery requirements remain the same as before.
Situation
Due to increasing current requirements with MerCruiser gasoline EFI or MPI engines, MerCruiser has changed the minimum battery requirement for all of these engines.
New minimum: 750 cca, 950 mca, OR 180 Ah.
NOTE:
When selecting a battery, any one of the ratings must be met. It is not necessary
to select a battery that meets all three ratings.
