Battery for outboard

30boat

30boat

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A friend has just bought an electric start outboard and doesn't know what size battery he needs .It's a 25 hp 2stroke Mercury.
Could somebody help?
Thanks in advance
 
Just a suggestion, but I would imagine that a 12-15 Ah m/cycle battery would do the trick. I await correction, but my 550cc 4-stroke 60hp m/cycle has such and it fires up no problem every time.
 
The owners manual will recommend a battery based on CCA size. You dont give any model details but the manual I looked at says 350CCA. I would think that more than adequate.

The smallest car battery you can find perhaps or a 12 volt motor cycle battery as suggested may be adequate.

Hopefully the engine has a changing coil and rectifier fitted but it is not likely to be bigger than 6 amps. It may well be unregulated though. If so avoid a very small capacity battery or you will be tending to overcharge it. For the same reason choose a non sealed battery that can be topped up when necessary.

If the battery is required to run any other electrical equipment on the boat then a leisure battery might be a sensible choice.

If your friend has mislaid his owners manual you can down load one from the Download Center at http://www.brunswickmarineemea.com/homepage/welcome


BTW be very careful not to connect the battery with the polarity reversed. Reversed polarity = instant death to rectifiers.
 
Last edited:
30boat said:
A friend has just bought an electric start outboard and doesn't know what size battery he needs .It's a 25 hp 2stroke Mercury.
Could somebody help?
Thanks in advance
Click to expand...
Years ago on my varied ski boats, there used to be fitted 85 amp hour ones, plenty of umph when the bloody things wouldnt start. In theory a motor cycle battery might start it BUT lee shore and it wont start, put a big one on!
Stu
 
skipper_stu said:
Years ago on my varied ski boats, there used to be fitted 85 amp hour ones, plenty of umph when the bloody things wouldnt start. In theory a motor cycle battery might start it BUT lee shore and it wont start, put a big one on!
Stu
Click to expand...
I run a 20HP off a 21 Ah jump start pack. It starts fine, and even after serveral minutes of trying (doh! connect the kill cord) will still start it. It probably has a pull cord permanently fitted so even if the battery fails you can still get going. (My battery has survived 3 yrs of misuse - stored outside for a year, stored in unheated shed for the rest; sitting idle for upto 2-3 months at a time then used a lot over one week/end then idle again for weeks etc - trickle charged once).
 
RIB_imposter said:
I run a 20HP off a 21 Ah jump start pack. It starts fine, and even after serveral minutes of trying (doh! connect the kill cord) will still start it. It probably has a pull cord permanently fitted so even if the battery fails you can still get going. (My battery has survived 3 yrs of misuse - stored outside for a year, stored in unheated shed for the rest; sitting idle for upto 2-3 months at a time then used a lot over one week/end then idle again for weeks etc - trickle charged once).
Click to expand...
Look at the post again, lee shore, trouble starting, for the sake of a couple of quid more you get peace of mind.
Stu
 
Battery

Around here and I am sure in UK the cheapest battery is a typical popular small car battery. Cheapest because they are most in demand. And ideal for what you want ie plenty of starting current. A salesman might try to tell you you need a "marine" battery to take the shocks received in boat motion but I suspect a car would have more vibration. good lcuk olewill
 
Surprised Refueler has not chipped in with his usual advice namely to get one from a breakers yard. :D
 
skipper_stu said:
Look at the post again, lee shore, trouble starting, for the sake of a couple of quid more you get peace of mind.
Stu
Click to expand...
Sorry stu - just realised you replied to me specifically...

(1) The point of my post was that I routinely start a similar sized engine with a much smaller battery than you were suggesting, without it getting any TLC. I have never had a problem with battery "juice".
(2) Almost all 25HP engines will have pull start. On any small engine this will be as reliable or betteir than an electric start. Electric start is for convenience - not for safety on a small engine - otherwise twin batteries would be recommended as is common on "mission critical" larger outboards.
(3) IME battery size is not the problem with outboards failing to start - it is usually corroded cables/switches which are voltage rather than current/capacity issues.
(4) if everything on board a small boat was "upgraded" for "peace of mind" you would end up driving a bigger boat with bigger engine!
 
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