Dual Battery on 21V - pictures??

First time owner, would like to install 2nd battery in my 2009 21V.

Current plan is to get a surepower 2315 and wire it to 2 blue top optima batteries.

I have a single battery in place from the factory. I'm not sure where the best place to put the second on in - very leery about starting to drill holes into a boat.

The boat already doesn't seem like it has enough space to store stuff - we have a pair of water skis and a slalom ski that only seem to fit in the area where the battery is and if I put another battery in there not sure things will fit. Also not sure whether to mount the surepower unit on the flat wall in the middle, or the little "bracket" that sticks out.


I would really appreciate it if anyone can post where the factory installs the dual batteries or any other installs in a 21V.

Other suggestions also appreciated greatly - I know this is a frequent project but as a first time boat owner it's a little overwhelming and scary.

First off you are going to love that boat...........

I will do my best to try and answer your questions but keep im mind there are many ways to do what you are asking.

First off on your storage problem I would suggest to get other board racks to store your skis, surfboards, kneeboards etc and get them out of the way as there is no need to store them inside the boat taking up your storage space, there are many options if you do a little searching on the net.

Your battery location can be next to your current battery installed in the boat and the sure power can also be installed in the same location.
There is no harm in drilling holes in the sub floor but I would use some silicone on the screws to keep any water from leaking into the hull but shouldnt be a problem if you use the correct length screws.
Another option as I have done is to put the battery in the rear storage locker ( I have one on each side left and right locker to run my audio equipment).
This also helps with ballast in the rear if you need more weight for surfing.

I am not trying to steer you away from the sure power but I have used them in the past and they work well but I prefer to use a perko switch this is a manual switch that you choose what battery the boat charges, the sure power will charge the main starting battery until it is fully charged then swap to the second battery to fully charge it mainly to keep the starting battery charged at all times.
I have had a battery go bad and did not know it so the sure power never switched to charge the 2nd battery leaving me dead in the water.
Its kind of what you get used to and both will serve you well.

Installation of either sure power or the manual type switches are fairly easy if you are a little mechanically inclined.

As far as battery selection I am not a fan of the optima batteries mainly do to the price and I haven't had them last any longer than a good name brand battery and you can buy two for the price of one optima.

There are a lot of good people here that will be glad to help you so remember your not alone.

Have a great summer........

You will be very happy with your new Supra.......

Well the boat does have the z5 rack, so I can put stuff up there when riding, but when trailering it can't be there and I'm not sure where else it would go storage wise.

How do you run the wires putting the batteries all the way back there?

I guess I'm confused about the comment on silicone - in the middle of my boat there is a large area with a sac and currently water/antifreeze. I assumed this went under the edge of the boat as well (under the battery area). By your comment I'm hearing that I'm wrong in that.

If I'm going to mount a battery tray - are there certain size screws or types of screws to use and I assume under the carpet is fiberglass, not wood so pre-drilling is always needed?

This is our first family boat and my kids are asking every day when we'll be able to go out and use it, we're super excited.

You can buy other tower storage racks that you can trailer with them out of your way.

There are plenty of online diagrams on the different ways to wire two batteries using a manual or automatic (sure power) type switches.
It would take me half the night to tell you how to exactly do it and will be much easier if you are looking at a diagram.
You can mount the second battery next to the one that is currently installed, this will be your least expensive way to do it.

Anytime I use screws that I screw into the floor or anywhere for that matter in my boat I like to put a little silicone on them to seal them. This will stop moisture from seeping in to the holes.

As far as screws and hardware I always use stainless and when mounting something into the boat I do like to drill a pilot hole.

The last battery tray I purchased came with the mounting hardware I just bought stainless screws to replace the ones that came with it.

And yes you can drill down into the carpet and screw directly into the floor.


Hope this helps,

I have an 09 21V with Z5. I strap the skis on the Z5 when on the water. Store them in the center locker when trailering. The factory location for dual's is side by side perpiindicular to the centerline of the boat on the raised portion of the floor in your storage area. The most critical aspect is make sure you install a negative lead connecting the 2 batteries. You will have an open ground otherwise and it will cause you fits. I am not a big fan of moving the batteries aft. You want to keep your cables as short as possible. You will have charging issues and ground loop noise on your stereo if you install long cables. Primary positive and negative to starting batt. Everything else to house battery. Also, recommend staying away from Optima's unless you can keep them topped off all the time. If they discharge all of the way, they don't come back easily. I have replaced alot of Optima's for people because the alternator on the Indmar's barley keeps up with the engines demands. An onboard charger is a great idea, but how you manage the use of your power has alot to do with it as well. If your boat didn't come with a voltage sensing relay battery selector (standard with factory dual setup), I would recommend one. If you use a standard Perko switch, you will have to manage which battery is charging throughout the day or your amps will drain the house battery pretty quick. It is a pain to have to keep switching them yourself. If you try to keep the selector in BOTH, your alternator won't charge either fully.

My boat is in a friends garage. I may be going there tonight to work on a fuel gauge issue. If I do, I will snap a picture. If I dont make it there tonight, I'll be on the boat this weekend, and will snap a picture. Our batteries sit side by side in the area immediately below the radio head unit.

here is a pic of my 21v no bats but you can see the trays
http://farm3.static.flickr.com/2745/...e23344a5_z.jpg

That picture is very helpful - I figured side by side like that would be the best way to go.

I wasn't aware I could store anything in that center compartment. That would take skis nicely, just worried about putting them on top of the ballast bag.