Battery Life on water

Question for those of you with two batteries, I was out Friday night, playing music loud (one amplifier) and with all systems on but only refrigerator running.

We swam for maybe 2-3 hours tops, and everything fired up as normal, started underway at idle in shallow water, then both alarms kicked in, and the battery dropped to 8V from 10/11 with alarms. Switched the battery switch to both and everything was fine. Got boat on plane, and switched back to battery 1 to fully recharge it.

Now this happened last summer a few times, so I replaced the batteries due to the old ones being 6-7 years old.

Granted we typically do the same thing for a longer period of time, and typically dont have this problem, and havent this season until now.


I am running two 1 season old Interstate Deep Cycle batteries. I try to treat battery 2 as an emergency only battery.


Does anyone else run into this? Does anyone think that the battery could be failing?

Well to be clear, you are running all that on ONE BATTERY ?

The other is / should be SAVED for Starting correct ?

Amp going hard and Fridge could drain a battery in 3 hours for sure....but you can get the battery load tested for sure to find out if the battery is dead or not. (or dying)

Amps can draw a very large amount of power along with the fridge.
By all means have the batteries load tested.
I recommend you do not switch battery switches while an engine is running, the alternators do not like it.
There has to be somewhere for the power to go or you burn out the diodes in the alternator.
Very few battery switches have an alternator cutout built in.

The refrigerator is a battery killer. It is best to have minimal stuff running while at anchor. You should be on just one of the batteries (which it sounds like you were) to always have a good one for starting in case you run the other one down too much. When anchored for 3+ hours, I will typically run the engine(s) at a convenient (i. e. safe) time for about 10 minutes to make sure to add a little 'juice' back into it.

Thanks for the input. I will defiantly load test the 1st battery, haven't had an issue once all this summer. Just seemed odd that it died so quickly.

I always run one battery at anchor, and leave the 2nd for starting.


Thanks for the input, seems like this could just be a normal condition.

i've sold substantially more batteries in summer than winter.
Heat kills electrical devices and a battery qualifies.
Probably normal condition.

If you have the room, Get a third battery and add it in parallel to the battery you like to use as the house battery. This will double your amp hour capacity for that bank. Make sure you use identical batteries. Does your 280ss have shorepower and a battery charger?

Just checking, for us cruisers with onboard gensets, we can just run the gensets for a bit, right?

tpenfield said:

The refrigerator is a battery killer. It is best to have minimal stuff running while at anchor. You should be on just one of the batteries (which it sounds like you were) to always have a good one for starting in case you run the other one down too much. When anchored for 3+ hours, I will typically run the engine(s) at a convenient (i. e. safe) time for about 10 minutes to make sure to add a little 'juice' back into it.

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It's normal for a boat to have substantially more hours on the gen than propulsion engines but make sure you and anyone you're next to has an up to date CO detector.
We have rafted next to boats that set our detector off but our gen was not on.