Anyone any good with battery configurations? Shamrock Quay area! HELP!


New member
28 Aug 2003
Hi all,

Spent all day Saturday tinkering and doing all those "fun" job before the new season gets rolling.

But I am now really confused about my battery configurations.. and I need help ASAP.

I have 1 large deep cycle RV battery (thought this was the starter batter)
and 2 smaller 85ah betteries sat next to each other (thought these were for domestics)
I was having real trouble with the domestics only lasting a short time so I decided to change the 2 x 85ah to 2 new 85ah leisure batteries.
I have a 1, 2, ALL, off isolator, so i decided to try and work out the best way to enure I was always able to start, even after a lazy afternoon in Newtown,

So.... with the large deep cycle connected permanantly

turn dial to "all" with neither 85ah's connected and no domestics and no start
Connect battery 1 85ah and use setting 1 I get domestics
Connect battery 2 85ah and use setting 2 I get domestics
Connect both 85ah batteries and select "all" I get domestics

But the engine only starts if at least one of the 85ah's is connected. and I can't remember if "all" has to be selected to get started??

So does this mean that both my starting and domestics run from the 2 85ah's?? If so what is the large deep cycle one for? Someone said it was an inverter battery, but I don't think I have an inverter??

I would have thought, the 2 85ah's were for domestic so u could isolate 1 and 2 or have both.. and the engine battery was purely for starting so would always get you home???

I am soooooo confused, can anyone help or recommend anyone?

I am based out of Shamrock Quay, but really need to get this fixed before the Easter weekend as we are away on her and then leaving her at her new home at Haslar..

Any ideas? HELP!




New member
11 Dec 2004
Amble, Northumberland
This is a bit confusing but will have a go.

First question do you have anything on board that looks like a domestic 13amp socket. If yes then with your shore power disconnected try plugging in a domestic appliance with a very low power consumption e.g. a mains powered portable radio. If you don't have an inverter it will not work. If you do it will work providing the inverter is big enough to carry the load, which it should be for something as small as I have suggested.

If you have no 13 amp sockets do you have anything that looks as though it would run on 240volts only - maybe a fridge?

Other ways to find out what the deep cycle battery is doing - does anything work when you disconnect the other two batteries - do you have an eberspacher - sometimes these are wired direct to the battery - even though they should not be

Is the deep cycle battery being charged? - is it connected to the alternator.

From what you say I think the deep cycle does not fit with the rest of the setup.

The 2 85ah batts are not big - 1 would be Ok to start say up to a 50hp motor but to rely on the other for domestics does seem odd and in any event the norm would be to use your deep cycle for that, subject to capacity.

Have you had this boat long - do you know the battery installation history? will your battery box accommodate 2 deepcycle batts and 1 85ah. Maybe someone has been messing around before you started.

Kind of think that if you can exclude the involvement of an inverter best way forward is supply position 1 on your battery switch with the best of the 2 85s and make this your start battery and supply position 2 from the other 85 and the deep cycle. This will give max capacity for domestics


New member
1 Mar 2005
Vancouver, Canada
You do not say if you have a single or twin engine or if it previously was a twin.
Normally 2 x 85a/h would be to start 2 engines and a deep cycle would be for domestics (house). If you DO have an inverter then a deep cycle should be used to power it. Deep cycles are normally reserved for domestics as they can be drawn down deeper and recharged without prejudice, whereas start batteries are high CCR's and are only used to give that one-off start.

If you have a single engine then both your 85a/h should be tied together in parallel and connected to pos 1, or, if space permits get a larger single 'start' battery. The deep cycle should be connected to pos 2. You should run the boat in the ALL position and, when stopped, go to pos 2 and use the deep cycle for your domestics, thus preserving your 2x85a/h bank for the next start.
To start the engine again go to pos ALL and run. However, if you believe your domestic battery is REALLY low you might go to pos 1 to start, then go to ALL after start, but make sure you do NOT switch to OFF.
Only ever select OFF with engines stopped.