Is my battery dead (failed) or not?

[BobW]

You cannot depend on your hydrometer

to tell you the state of charge of the battery unless you have been reading them since the battery was new, or you have baselined the battery to know for sure the reading at full charge with a known level of liquid in the battery.Consider this: Your battery is fully charged, you take a hydrometer reading and get 1.290. Is that good or bad? The answer is that it depends on the electrolyte level. If the level is down and you fill each cell up to the top, the reading will (after it mixes) probably be 1.260.So don't depend on the hydrometer to tell you much, unless you know a lot about the batteries.Cheers,Bobs/v X SAIL R 8

 

[BobW]

Jimq26 I think the consensus is to replace them

IF they are bad. In your original post, you stated that the hydrometer indicated that 1 cell in each battery was bad. May I ask what the readings were?2 more points: 1. The best way to test the batteries is to take them to an auto parts store and have them put them on the tester. That will be pretty conclusive. Unfortunately, if they are indeed 8D batteries, you had better be in pretty good shape 2. For lake sailing in a 28 foot boat with an outboard (that has a back-up rope pull) and probably not much equipment to pull current, you have WAY more battery power than necessary. Keep what you have as long as they are good, but when you have to replace them, consider 2 factors: PRICE and WEIGHT. Do you really need to spend a couple hundred extra dollars to haul an extra 130 pounds around your lake?'Nuff said.Cheers,Bobs/v X SAIL R 8

 

[flyhop]

Good points, all

Outboard does have an emergency rope pull-starter, so good there.My point about hydrometer readings was that each battery had 5 cells reading in the green, and 1 cell in the red. Didn't get specific readings as I knew I didn't have a baseline. Just seeing if there was a big difference, and the readings were taken after 12 hours rest (batteries, not me). Yes, you are all correct, 2 8-D batteries is way overkill, but the boat came with them so I'm just trying to keep the ones I've got without having to dump more money in.I'll use the boom and a comealong to get those hoss' out of the hold and haul em to Autoparts store. Thanks again.

 

[Jerry]

parallel vs. separate

If I were to have two batteries aboard, I'd keep them separate unless you need the combined available amps. The reason being that if one battery fails while being wired in paralell, it will discharge the second battery leaving you with two dead batteries! With Murphy out there -- at the worst possible time.

 

[flyhop]

Oday 28 electrical panel...response

From reading I've been doing, the panel I have includes a 1-2-both-off switch. If I understand it correctly, the both position puts these batteries in parallel, while the 1 and 2 positions isolates each battery. What is a little wierd is that the outboard will start with the switch in ANY position, including the off. This leads me to believe that the batteries are hard-wired together in parallel before the switch, and that the outboard is directly wired to one of them. I really haven't gotten into the wiring of this boat. It is a pretty high priority on my winter project list.

 

[Dan McGuire]

Good Argument Both Ways

There is a good argument for keeping them in parallel or isolated.A lot of this has been covered. If you are keeping them in parallel, they should be well matched batteries. Buy both of the same brand and type at the same time. If one fails, it will tend to kill the other one. A major reason why I occasionally run one at a time with a trolling motor, is that when the first battery runs down, I know fairly accurately how much capacity is left in the second battery. As an alternative to that I occasionally run the motor until the voltage drops below 11V under load. I then switch to the other battery and use it. If it drops to below 11V, I then switch them on in parallel and realize, I don't have much left. The big advantage for keeping them together is that, if you are carrying a big load, for example larger than C/10 (Battery Capacity/Rate), the two batteries in parallel will deliver more capacity than one at a time. There are several reasons for this. At the lower rate, the battery can utilize more of the active material. There is less wastefull heat and there is less voltage depression do carry the load itself.On that C/10. That is a somewhat arbitrary number. The lower the rate the higher the capacity. To use the C/10, if you have a Type 24 battery with about 75AH capacity, don't run it above 7.5A if you want good capacity. In my case with the motor demanding 30A at max speed, that is about twice C/10 with both batteries on line or four time with one battery on line.

 

[BobW]

Flyhop, I think you're right....

and you need to check the wiring. If those batteries are wired around the switch, you will probably want to change the wiring to route it through the switch.The exception is when there are diodes in the wiring to the motor.... a diode will only allow current to flow in one direction (think of kids and money ;DI can't imagine why anyone would bypass a perfectly good switch, but I also can't imagine why they would have installed those 8D monsters in your boat, either It would be a good idea to check out the wiring and charger and get everything figured/configured before you invest in replacement batteries.Cheers,Bobs/v X SAIL R 8

 

[mjmoyer]

Battier's 1, 2 or 3 how many do I need?

Believe it or not, I carry 3 battery's on board, the n4 is for the yanmar Diesel 20 hp. the other 2 is a group 28 750 cranking amp's to run the aux items. lights stereo ect... navigation and thing's. my problem is my #1 bat. is having a drain on it, How do I isolate the problem:

 

[BobW]

Check the wiring.

You'll need to trace where each of the wires from the Positive (+) terminal goes from the #1 battery. Those are usually red wires, but not always.You haven't given much to go on. There are usually 2 sources of charging (alternator and shorepower-supplied battery charger) and at least 2 loads (starter motor and DC distribution panel) but that is extremely general. There is also at least 1 switch (commonly an orange 'Guest' Off-1-Both-2)Again, this is very general stuff. You'll need to trace out your wiring and hopefully draw your own wiring diagram for future reference.Two other less-likely possibilities:1. You didn't mention time frame, so it is possible that if your #1 battery isn't hooked to anything but the engine alternator, it could be self-discharging. That happens over a period of weeks/months depending on the type of battery (You called it an n4 - I can't find that)2. Water spilled on top of the battery could be creating a path for discharge. Batteries should be kept clean.Hope this helps, even a little bit. If you can find out more information, we can possibly be of more help.Cheers,Bobs/v X SAIL R 8