Battery Confusion..

Don S/V ILLusion · Jul 27, 2023

Whoever told you that (keep the switch on both) is wrong. You just experienced why - you depleted both having nothing in reserve to start the engine. The ‘both’ position should be used only when charging off the engine.

Dont buy so-called marine batteries. Batteries are batteries; adding the “marine“ label is nothing but an excuse to charge more money. Your choices should be either start battery or deep cycle battery, the latter type will serve you well for both power use and as a start battery. Conversely, start batteries are good for only one thing - starting.

Richard19068 · Jul 27, 2023

+1 on Don S/V ILLusion's response

Also, you will want to know how many amps your fan(s) and lights draw to make sure you don't overdraw the battery you are using for the "house bank". Know that you generally do not want to use up more than 50% of the battery's amp hour capacity.

Lots and lots of information available if you search this site for "power budget".

How will you recharge the batteries? Solar is a good possible option.

JoeWhite · Jul 27, 2023

Installing a 100 watt flexible solar panel and charger is a good idea when shore power is not available. Not much electrical knowledge is needed.

jviss · Jul 27, 2023

Would be helpful to know how you charge. It I was solving that I'd look for a single LiFePo4 battery with a low voltage disconnect.

Tally Ho · Jul 27, 2023

Jtcf78911 said:
Hi. This is a simple ask...so please bare with this relatively new boat owner. For background, I have a 1985 O'Day 28 that lives on a mooring ball, never uses shore power, etc. with two batteries and the standard 1-2-Both battery bank options. At nights on the boat I will run inside lights, a small fan, and a converter to charge phone, etc., but that's about it. Recently I fell asleep with fan running and lights on..and a jump was then needed to get her to start again. Prior owner said I should just always keeps the battery switch in the Both postion - which I have... I'm looking at replacing batteries, but not sure if should just be buying two basic marine starting batteries, a marine starter and a deep cycle, or just two deep cycle. As my electrical use is simple...would like solution to be the same....though I would like to be able to use my fan all night without draining all my power... Thanks. Capt. Tom.

You might have been told that for charging the batteries…if your wiring is set up to charge back through thr 1-2-both-off switch, you need it set to both so both banks charge. But you have learned it is not best to drain them both.

I would guess that those batteries must have been pretty tired to drain with what sounds like a fairly small load (no fridge…which is a big draw).

I switched to 2 6-volt golf cart batteries a few years ago, providing about 215 AH at 12 volts. Enough for me to anchor overnight for 2 nights (maybe a little motoring during the day). And that includes running my fridge.

I don’t have a separate start battery (it is on my list to get to…) haven’t been stranded yet on the occasional overnight on the hook.

It takes a little extra wiring to use the 2 GC batteries, but hard to beat the capacity/deep cycle capability of these lead acid batteries For the price. I got mine at Sam’s Club on sale.

Greg

Timm R Oday25 · Aug 2, 2023

While I agree with everything that's been already posted , I humbly offer a few thoughts . Our 12 volt fans (2) use less than
1 amp each . If your batteries were both discharged ,I would hazard a guess you have several issues.
The first being ,one of your batteries was older and therefore had less amperage capacity . This lead to the newer "healthier "battery
trying to equalize the older. The other thought is that you didn't have the reserve amperage you thought .
We use two deep cycle 12 volt batteries . One is charged by a 20 watt panel . Max amperage is maybe 1.6 . The other is charged by the outboard , and a 10 watt panel
Even that is 4 maybe 5 amps at wide open throttle.Even with a chartplotter ,a stereo and an autopilot we rarely drop below 12.3 volts .
We've spent as long as week like this . Led lights are used and we have no refrigeration

jssailem · Aug 2, 2023

Timm R Oday25 said:
Led lights are

A great modification to the traditional lights used in boats from 80's.

@JoeWhite and @Richard19068 's suggestion of a solar panel is excellent for the mooring buoy set up you have.

@Don S/V ILLusion and @Tally Ho nailed the issue that confuses new boat owners about 1-2 or Both switches. @Stu Jackson has a wealth of knowledge regarding the challenges. Search for info about 1-2Both switches under his name.

Boat electrical systems require the owner to become proficient in a new skill. There are no shortcuts. Your experience with the guidance from the Previous Owner should be evidence about that. One of the experts that has shared his vast knowledge about marine electrical systems is a fellow member @Maine Sail . On his site is this material 1/2/BOTH Switch Considerations
If you find it helpful I would encourage you to send a donation of thanks. His site shares the difficulty that struck our fellow sailor a couple of years ago. Everything helps.

Good luck. You'll master this electrical issue.

Stu Jackson · Aug 2, 2023

jssailem said:
@Stu Jackson has a wealth of knowledge regarding the challenges. Search for info about 1-2Both switches under his name.

Here are the highlights. These are from my
Electrical Systems 101 Electrical Systems 101 on the C34 website.

OEM 1-2-B Switch Wiring History Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams

1-2-B Considerations (New 2020 - Rod finally got around to diagramming what I had done in the above link in 2009

)
1/2/BOTH Switch Considerations

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowners.com/showthread.php?t=137615

This is a newer primer for boat system wiring design with a thorough diagram: Building a Good Foundation (October 2016)
Building a DC Electrical Foundation

Battery Confusion..

.

.

.

.

.

.

.

.

SBO Weather and Forecasting Forum Jim & John

.