Adding 2nd house battery in parallel on 2006 Hunter 38

Jan 29, 2010
64
Hunter 38 Ocean Gate, NJ
My Hunter 38 has one 4D house battery. This just isn't enough for our usage. I want to add a second 4D wired in parallel with the first so that I will maintain the 12V level but double the amp hours. I think it will fit in the generator compartment.

Has anyone done something like this? Will my 125 amp alternator charge them both as one unit? Should I add any venting?

Overall, what do you think of my idea?

Thanks.
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
I'm surprised you've lasted this long on one battery! We have 3. 2 house in parallel and 1 start. All on an ABC switch. Mainsail's website has good info for this project but I don't have the link.. The alternator should be okay but i assume an onboard charging system is in the future also.
 
Dec 28, 2015
1,837
Laser, Hunter H30 Cherubini Tacoma
I redid all my cables for my 4 batteries myself. Bought the crimper, lugs, cable and sheers on Amazon. Cost me about $100 and I got a new tool out of it with spare supplies. Just adding a battery would be around $50 assuming no fuses are needed.
 
Jan 1, 2006
7,039
Slickcraft 26 Sailfish
My 2002 H356 had 2 X 4D batteries. Both fit in the battery box that was OEM, I think. We had the standard alternator which, I believe, was 30 amps. I don't think it did much to charge the bank but we also had the shore powered inverter/charger which did the loin's share of charging. Venting is usually good as long as it doesn't end up being a source of water ingress - such as when heeling. .
 

jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
Connecting a new battery in parallel with an old one is generally not a good idea. Best if the batteries are new, and even from the same manufacturing lot. So, yes, it makes sense, but you should buy two new batteries.

You don't mention the type of battery you're interested in, or what kind of alternator regulator you have.
 
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Apr 11, 2010
946
Hunter 38 Whitehall MI
Not an expert at battery kinds of things so I’ll let others speak to that. I’ll focus on your location question

My Hunter 38 came equipped new for a three battery set up. I have 2 4Ds and a starting battery.
The compartment under the cabin sole right in front of the nav station holds 1 of the 4Ds and the starting battery. The second 4D is located under the forward part of the port settee.

The 4 Ds constitutes a single bank.
There are two battery switches in the compartment built into the side of the nav seat (where the main breaker for the windlass, DC master, and the circuit breakers for the bilge pump, smoke and CO detectors and the echo charger). My battery charger is located under the nav seat.

There is no special venting in either location.
 
Jan 29, 2010
64
Hunter 38 Ocean Gate, NJ
My current 4D was bought this spring so it is a new flooded dry cell. I will get another of the same brand. The alternator is a 125 amp Balmar with a Balmar 3-stage smart regular.
 

jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
My current 4D was bought this spring so it is a new flooded dry cell. I will get another of the same brand. The alternator is a 125 amp Balmar with a Balmar 3-stage smart regular.
Sounds good to me!
 
Nov 14, 2005
12
Hunter Hunter 38 Ventura Harbor, CA
My 2005 H38 has 2 6V house batteries in parallel and the start battery under the floor next to the nav station. It also has 4 6v batteries under the settee in front of the sink positioned next to the water heater also in parallel together.. (The PO took her to Mexico). Battery charger is under the settee in front of the nav station along with the Bose amp. The batteries are all tied together. The alternator is stock. All of them from Costco.
 
Jan 29, 2010
64
Hunter 38 Ocean Gate, NJ
To Quadrill38: Do the two battery switches have only on and off positions?
 
Feb 10, 2017
305
Hunter 41 Progreso
bad idea to combine an old battery whit a new one, the new one will never charge to the top because the old one is telling your regulator to stop sending charge before time.
 
Feb 10, 2017
305
Hunter 41 Progreso
a normal battery that you can add distilled water to keep the plates under the acid
 
Jul 23, 2009
857
Beneteau 31 Oceanis Grand Lake, Oklahoma
I was just being a jerk.
No such thing as a flooded dry cell.
I'm sure he has standard flooded cells. FLA
 

Twille

.
Oct 8, 2012
63
Hunter 38 Henderson, nc
On my H38 i changed from 1 4d to 2 8G8D’s. No issues, placed one in the normal spot (under the Nav station and one under the settee in front of the sink. Pull 3/0 cable to the ground bus and put in a positive bus to connect the batteries to. 3/0 to the on off switch —- which isn’t true on a Hunter. Anyway works great!
 
Oct 29, 2016
1,915
Hunter 41 DS Port Huron
As important are the batteries one must also consider the cables which are connected to them the bigger the better, minimize voltage drop and maximize charge efficiency. When I redid our batteries (6 x 6V Trojan 125) and charging system, I followed the advice of @Maine Sail and ran new cables direct to and from the Balmar alternator. I have also read that matching cable lengths is an important consideration as well, equalizing voltage drop. I my case the cables were run with 2/0 marine grade (tinned copper). Genuinedealz.com is a good source for custom cables.
 
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