Dead Battery on Pontoon Boat

[Boatmanswife]

Hi Guys, I have a 1980's 40 hp Mercury outboard on a Starcraft Pontoon boat that I recently purchased. The battery was new last year. It hasn't seen much use. Yesterday we spent a great afternoon, about 5 hours cruising slowly around the lake. The only electrical accessory that was on was a fishfinder. The boat and motor worked great. However when we returned to the dock, the engine stalled as I pulled into reverse, at that point the battery seemed dead (just a click at the key) and no power. Is it possible the fish finder would have run down the battery even though the outboard motor was running the entire time? We ran the motor at top speed for about 15 minutes on the way home, the rest of the time was trolling speed. I appreciate your thoughts.....

 

[Silvertip]

Re: Dead Battery on Pontoon Boat

Whether a battery is new or not has nothing to do with whether it is charged or not. Infrequent use is death to a battery. 15 minutes of running with an outboard is not enough to keep a battery charged.

 

[Boatist]

Re: Dead Battery on Pontoon Boat

All batteries self discharge so must be charged once a month in summer and every 2 months in winter. If you do not keep it charged and fully recharge at the end of each trip then it will not last more than a year.

A 1980 40 HP Merc probably uses a stator to charge with and puts out very few amps at low rpms.

I would fully charge the battery as soon as possible then check the voltage with no charger and the motor turned off. It should read 12.6 volts. Then start the motor on the water or on muff and check the voltage again. It should read 13.8 volts for good charging. If it does not read 13.8 volts at idle then speed up the motor and see what it reads. Then turn your fish finder on and check again.

Fish finder usually only draw 2 to 3 amps but at low RPMS I am not sure a 1980 40 HP motor would put out 2 to 3 amps at low RPMS.

One thing for sure if you do not keep your battery charged then you will be lucky if it last more than a year. Fully charge right after each trip and keep charged between uses and it should last at least 6 or 7 Years.

Charge with a smart charger or a automatic charger or an onboard charger which will fully charge without over charging. How batteries are keep charged will determine how long it will last.

Good Luck

 

[Boatist]

Re: Dead Battery on Pontoon Boat

All lead acid batteries self discharge. need to charge once a month in summer and every 2 month in winter. If you do not keep charged then plan on buying a new battery every year.

Still if it started in the morning and ran the motor most of the day then it should have charged some. I do not know the output of a 1980 40 hp merc but I think it should be more than the fishfinder used. Fish finder normaly only 2 to 3 amps. Maybe that old of a motor does not put out much current at slow speed.

I would fully charge your battery with a good automatic or smart charger then check battery with a volt meter. It should be 12.6 volts. Then with the motor on muff start the engine and check the voltage again. If it is charging good the voltage should be about 13.8 volts or more. If it is then turn your fish finder on and check again.

Check for loose or corroded battery cables.

A 1980 40 HP may use a stator to charge instead of an alternator. If so then may not put out much charge at low RPMS.

Anyway always keep your batterty charged if you want it to last 6 to 7 years.

Good Luck

 

[Boatmanswife]

Re: Dead Battery on Pontoon Boat

Thank you for your advice guys, I really appreciate it.