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Basic Battery Question

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brrit
1st Mate

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80 Posts

Initially Posted - 10/19/2007 : 23:16:32

Ok... I'm sure there is a very scientific & analytical answer to the following question, but I was wondering if there is a basic rule of thumb here.

I have 2 enclosed gel batteries. Tonight we went out and ran two lights inside the cabin and the running lights for about 2 - 2.5 hours total. After this time, the batteries were unable to start the electric start 9.5hp motor.

To me, it seems like the batteries should be able to handle this type of load pretty easily. No radio. No electronics running. Just a couple of interior lights with the running lights. Do new batteries need to go on the Christmas wish list?

And, how long would be a reasonable time frame to run a couple interior lights with my running lights and still expect the electric start to crank up with the motor? I would think 4-5 hours pretty easy. Are my expectations just too high for the batteries?

Thanks!

Bryan Ritchie
"Serenity Now"
1989 C-25 TR/FK #5829
Dallas, Texas
www.athomewithdad.net

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delliottg
Former Mainsheet C250 Tech Editor

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4479 Posts

Response Posted - 10/20/2007 : 02:10:15

Bryan,
Your batteries should be able to withstand a lot more load than a few lights for a couple of hours. There are a lot of things to be considered, but basically it sounds like new batteries may be on your shopping list. If you're interested in figuring your electric load, lots of us on the forum can help. Here are some questions about your batteries:

How often do you charge them? When they're fully charged, what is the voltage? If you get much below 11 volts your batteries are very depleted. A full charge will show over 13 volts.
Is your engine charging system hooked up properly?
Do you use a solar panel to keep them topped off? (this works very well for us).
How old are they?
Do you have a way to separate them so you can use one as the "hotel" load (lights, etc.) and one as your starting circuit? This way you can safely run down one battery while maintaining a starting battery. This does cause some charging complexity though.

I would expect for a pair of batteries in good condition that you should be able to easily run your lights all night & still start your engine easily in the morning.

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piseas
Former Treasurer

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2017 Posts

Response Posted - 10/20/2007 : 12:52:08

I had a similar thing happen to me. I have 2 batteries and had only the anchor light on all nite. The next morning, I was not able to fire up the engine with electric start. I couldnt understand why.
Well I happened to talk to PO short time after that and he asked me if I had used the shore power he installed on boat. I said I had not. He said charging the batteries with just the engine was not enough and I should use the shore power when docked.
Do you have shore power?
Steve

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brrit
1st Mate

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Response Posted - 10/20/2007 : 15:18:02

Thanks for the responses guys. I'm about to head about and check the voltage on the fully charged batteries.

I am using shore power to charge the batteries each night. So, if I'm not sailing, the batteries are charging (at least in theory they are charging). No solar panel on the boat for recharging.

I'm assuming the battery charging system is hooked up properly. It definitely charged the batteries from a lower charge earlier this season. I'm assuming it is working.

I've heard of isolating one battery for use on the water and switching to another for firing the motor, but thought it was unneccessary for limited use on an inland lake. (Maybe not. This might be the way to get the batteries through another few months without new ones.)

Thanks again for the responses. I'm off to pick up a voltmeter and see how well these batteries are charging.

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Dave Bristle
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Djibouti
10005 Posts

Response Posted - 10/20/2007 : 15:50:32

Make sure your charger is appropriate for gel-cell batteries. They require a slightly lower max voltage than flooded batteries, and can be damaged by too much voltage, as they are likely to get from a charger not set up for them. Your charger should have a setting for gels--if not, it's probably not the right charger, and may have damaged the batteries.

If you do replace the batteries, I recommend AGM over gel--all of the same benefits, but more tolerance of fully discharging, and of normal charging voltage. Also, when not used, they hold their charge almost forever, so you don't need to remove them from the boat for trickle-charging in the winter, for example.

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Fantasy II
1st Mate

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80 Posts

Response Posted - 10/20/2007 : 18:14:10

This could be your problem, as it was mine. My shore power is connected to an old 20-amp receptacle at the dock and it frequently becomes disconnected by itself!

Others on my dock have tried many ways to keep the plugs from disconnecting (bungee cords, rope slings, etc) but none of them seem to be reliable. When I visit my boat it is only 50-50 whether my dock power has remained connected! The club has promised to replace the old receptacles in the near future, and we are all waiting for that to happen.

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piseas
Former Treasurer

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2017 Posts

Response Posted - 10/20/2007 : 19:39:22

Bill, good point. I too have come back to unplug shore power only to find out it was already disconnected. I dont know of any way to keep it plugged in but wil speak to manager about new recepticle. They have already given me a new utility box, not sure why they havent updated rest of it.
Steve

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britinusa
Web Editor

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USA
5404 Posts

Response Posted - 10/20/2007 : 21:21:29

Steve, also check wether your battery charger is designed to charge and supply.
ie. If it is charging the battery, can you also run stuff off the battery!

Ours (guest charger) does not allow that, it cost us a pair of new batteries and a new charger to find out.

In short, (no pun intended) if the charger is not designed to handle a load while charging, it can both blow the charger and the batteries.

Paul

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.