I just purchased a 1989 272 SR-1...two batteries with a single Perko switch. On # 1...I get nothing...when on all or 2 I get enouigh to crank the engines over... Actually enough to crank the starboard engine, but when I crank the port is stalls the starboard and dies.I crank the starboard again and she starts . After a few minutes and a few more RPMs the port fires up but you can hear the drain on the system.

I know the batteries are probably shot...it's the end of the season here so I don't want to buy new until spring..(maybe I can't wait )..
My question is this...When she starts the volt meters show 12 or just under on both sides. After running for 20+ mins its up to 13-15. I'm not sure what this is telling me. My other boat is a 1978 Donzi 21GT with a single 330trs all original and I've had it since '81....when the battery is low it runs at 15-16 and then comes down to 12-13 when charged up.
The formula gauge is different and I'm not sure what I'm seeing.
The donzi I've had for 37 yrs and I can tell you every inch of that boat in detail...This twin formula is new to me and I need some veteran advice. Previous owner had a larger sound system installed and suggested running stereo on 1 and switching to 2 for driving... Not sure if there was some botched wiring or not.... Going through her a bit at a time to make her mine....gotta learn all over again

So...when the volt meters show 12 is that a heavy draw on the alternators? (opposite the teleflex in the donzi?) I'm concerned the electrical system may be wonky.

Also, shore power? Does that charge the batterys when plugged in? Former owner has a 120V 3prong wire set-up for garage storage...said to leave plugged in? resources for that wiring that anyone can explain?

Please help
Thank you

peace
PK

Take batteries to Orileys and have them load tested.
Be sure to test on the terminals your system is connected to, ie. post vs. stud.
Here is something I learned this season about the screw (stud) posts. Only the threaded portion conducts, Not the base (I may have this backwards) . Why is this important you ask, I could not get enough power to crank motor, new batteries and tested 100%. I was using stainless hardware, washers and nut to attach the battery cables to battery. Tested the battery with the test unit connected to the stainless nuts, BATTERY BAD indication. Do not use stainless on any battery connection as they act as insulators.
After I fixed this motor cranks great.

I understand your other battery is functional. Please hear me out on this. I work on industrial equipment and see this mistake made far too often on customer equipment. If a system is using 2 batteries it is much easier on the charging system when they are the same size and age. As of now you have a one nice hot battery that is being drained by the old decent battery they will float together and in time ruin the new one as well. Replace both of them with the same and you will save yourself headache in the long run.

as far as the VDO volt meters. You should just just over 12v with key on not running. A good charged battery should have between 12.5-13v. Once running you should see very close to 14v.

Or, never run on "BOTH" except for starting
but Red is 100% correct.

not? Why not run on both?

I was in particular addressing the situation Redneck was referring to where the mismatched batteries "level out"
I have read before that you should not run on both but I don't remember the reasoning.

I always run on both. It charges both. When I get where I am going I select 1 for stereo play. When I get ready to leave I put it on both for starting and driving.

he is simply saying that with 2 different batteries you should run it on either one or the other not both because it will do as I stated above and balance causing the new battery to fail prematurely.

Thank you all very much!!
I will be swapping the other 'old' battery tomorrow for the same one.... as has been recommended.

Also, as has been stated....I plan to run and start on 2 batteries and then chill in the bay with the stereo running off 1 or the other. Seems logical to me.

Again...thank you all very much!