Should it charge?

[Ats666]

I've got an early to mid eighties 18hp merc (serial 7198298).
It's got electric start with controls.
Should it charge the battery while running?
I checked with my multi-meter and it was not.
I use a group 31 deep cycle as a starting battery and keep a trolling motor on board to get me home in case the main motor fails and just assumed till afew weeks ago that it was staying fully charged with the amount that I use the boat.
Was a bit shocked to see the battery voltage down to 12.18 with the motor off and 12.08 with the engine running the second last boating weekend.
Thanks guys

 

[racerone]

Charging kits were optional.-----Do you see a rectifier ?------Post some pictures of the port side of the block.

 

[Ats666]

Don't mind the dirt. Motor has been cleaned, lower cowl replaced with a good used one and weatherstripping replaced since photo was takin.

What would it take to add charging capabilities?
Thanks

 

[racerone]

It appears to have a charging system.---------That wee square part with orange plastic.-----Close up picture of that item needed.

 

[flyingscott]

Yes your motor should charge. The Orange square is a rectifier and there should be a set of coils under the flywheel.

 

[merc850]

I don't think that system will charge a deep cycle battery which requires a hi-amp supply; better to use a regular marine starting battery for the motor and keep the D.C. one for the trolling motor.

 

[Ats666]

Merc850 - The battery was fully charged when installed on the boat and there are no accessories to power installed on the boat. The trolling motor is just a back up in case the main motor dies and leaves me stranded, which it has never done.
Should it not keep the battery fully charged?

Racerone, flyingscott
Any tips or guides to follow for diagnosing the problem or should I order the service manual on eBay?
Thanks

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[flyingscott]

How old is your battery? The charging system in that motor will keep a battery charger but not charge it from dead. Take a volt meter and rev the motor up and see if the voltage goes up. Put the probes on the battery red to positive black to negative. You do not need to rev it much. You should see the voltage to up. Also take your battery and have it load tested.