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gosenbach
1st Mate

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USA
30 Posts

Initially Posted - 06/29/2015 : 09:20:24

Hi there.
As I am adding more and more electronics to our new boat (I have lots of upgrades and mods coming), I would like to add a second battery in parallel with the one I already have. Although I do notice that the access to the battery compartment is very tight, even though there appears to be plenty of room back there.

Has anyone out there patched in a second battery? Better to be run in parallel or installed as a second bank? Any concerns about enlarging the access opening to the battery compartment for easier access? I have some other components I would like to install back there as well like the solar controller, so more access would be helpful.

If you have done this on your boat, would you happen to have pictures?

Thanks!

Gregory
(Catalina 250 MkII WK #971)

Edited by - gosenbach on 06/29/2015 09:21:10

OLarryR
Master Marine Consultant

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USA
3463 Posts

Response Posted - 06/29/2015 : 10:18:13

There are various sources with responses on the web if you do a search in Yahoo or Google regarding your question. What I have read is that having two batteries is not like you will obtain twice the life of a single battery and if not hooked up with a battery combiner, it is possible that if one battery is weaker, even with charging, the weaker battery will draw down the stronger battery.

Having said that, my Cat25 came with two batteries and I always leave the batteries with the battery switch in the "Both" position. I never bought a battery combiner but I had what I considered good life out of my old batteries which the PO had for at least 1 year and I had for about 7 years before I decided to replace them when they probably had at least another year to go. (I had bought an AGM battery for backup for a bilge pump I installed in my sump pump tank at home when a hurricane was approaching. After the hurricane passed with no issues, I had a brand new AGM battery and so I bought another and replaced my old boat batteries.)

Larry
'89 Robin's Nest#5820, Potomac River/Quantico, Va
http://catalina25.homestead.com/olarryr.html

TakeFive
Master Marine Consultant

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2272 Posts

Response Posted - 06/29/2015 : 10:20:29

There's no one "best" way to do this. I didn't want the extra weight all the way at the stern, since I already need 300lb of ballast in my bow. Ideally I'd move a second battery (or both of them) to the bow, but that was too ambitious for me. I compromised by mounting the second battery under the companionway steps. Since I have a trolling motor for my dinghy, this makes it easily accessible if/when I want to move it to the dinghy (which I haven't actually done yet).

My wiring is just run in parallel. Selector switches add complication and potential to fry the regulator on the outboard if you accidentally turn to "off" while the motor is running. On larger inboard boats you might want to isolate a starter battery to make sure it's always charged. But with an outboard the worst that can happen if you run the batteries dead is you have to pull the starter cord once. Why worry? It's better for the batteries to have them share the load so their amount of discharge is cut in half, which prolongs their life.

Personally I would not cut a larger hole in the bulkhead. Why not just remove it when you need to work back there? (Mine is difficult to remove because of crap hoses between my head and holding tank, but most boats don't have that issue.)

I know that others have done it different ways, but that's my setup.

[EDIT: Both of my batteries are identical, with same date of manufacture. You don't want to connect batteries in parallel unless they are identical. Like Larry, I ended up with my extra batteries from an emergency sump pump. When I decided I wanted two batteries in the boat, I moved the two sump batteries to the boat and moved the old boat battery to the sump pump.]

Rick S., Swarthmore, PA
PO of Take Five, 1998 Catalina 250WK #348 (relocated to Baltimore's Inner Harbor)
New owner of 2001 Catalina 34MkII #1535 Breakin' Away (at Rock Hall Landing Marina)

Edited by - TakeFive on 06/29/2015 10:29:58

gosenbach
1st Mate

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USA
30 Posts

Response Posted - 06/29/2015 : 10:32:04

The blukhead comes out???? That would be awesome, here I just through the only access was via that 2foor wood cover back there. It would be way more convenient if the whole thing game off. I'll have to look next time I am out at the marina.

I think I will want to mount both batteries back in the stern. I'll have kids onboard and I don't relish the idea of having a big marine battery out where it can be played with while I am not looking...

Gotta be able to power up my radar.. that going to be an upcoming project in a few weeks.. :)

thanks for the suggestions!

*tinker tinker tinker*

Gregory
(Catalina 250 MkII WK #971)

Edited by - gosenbach on 06/29/2015 10:32:24

frog0911
Master Marine Consultant

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USA
1349 Posts

Response Posted - 06/29/2015 : 19:10:51

Here are some pic that might help you.

Frog and The General

C250, Pretty Penny II, #743
FLEET 25
Coronado 15, M-Cube, #3316

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.