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Old 08-03-2014, 22:52   #1
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What Battery Do I Need?

Hey guys, I recently bought my first boat! It's a 1975 Mac Gregor 23' with a 1986 Evinrude 9.9 electric start outboard. The boat came with a small solar panel but unfortunately, someone stole the battery!

Currently the only electronics on the boat are engine, bilge pump, and lights. I need a new battery and had a few questions!

1. The previous owner said he used a car battery in the boat? I was planning on going with a marine battery, whats the difference? Also do I need a certain voltage and amperage? I was thinking of going with this one EverStart 24MS Marine Battery: Automotive :

2. Will my engine charge my battery while running? Or do I need to add a rectifier or some other setup?

3. Later on I'd like to add a VHF radio, some interior lighting, and perhaps a small stereo (alarm clock size). Will I most likely need more solar panels, a generator, more batteries?

The solar panel is about 1'x6" should I leave this plugged into the battery at all times or do I need a regulator?

I'm totally new to this so thanks for any help!
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Old 09-03-2014, 01:12   #2
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Location: Salem, MA
Boat: Pearson 31
Posts: 535
Re: What Battery Do I Need?

Your outboard will not charge the batter.

If you want to install solar, read this:

The RV Battery Charging Puzzle HandyBob's Blog

If you have access to shore power (i.e., you have a slip and can plug in at the dock) and you don't have a battery charger on board, then you should read this:

Installing A Marine Battery Charger Photo Gallery by Compass Marine at

Personally, I would just use the outboard's pull start if it has one, and just use the battery for the lights and bilge pump. In that case, the solar you have might be enough. A group 27 battery would be more than enough, maybe a little overkill for this purpose.
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Old 09-03-2014, 12:32   #3
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Location: Kona, Hawaii
Boat: 1969 Pearson 35 #108
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Re: What Battery Do I Need?

You need a deep cycle battery not a car starting battery. Assume a 'marine' battery is deep cycle but would check the spec's to be sure. Would shoot for about 100 am[ hour battery. CCA is fine for starting battery but not a measure for your use.

The engine, since it's electric start, may have an alternator and be able to charge the battery. Check the manual or get out your trusty and test the voltage into the battery when it's running.

The solar panel is basically a trickle charger and shouldn't need a charge controller. Check the electrolyte level in the battery regularly. Shouldn't need topping more than every 6 months or sor. If the electrolyte is dropping down in a month or less, then a charge controller or disconnecting when left for long periods of time is in order.
Peter O.
'Ae'a Pearson 35
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