Extra house battery

[Hydraulicjump]

This is a lemonaide out of lemons question for those with an R-27. I was having a weak start battery problem, even though my flooded batteries are less than a year old. On advice, I replaced the start battery with a cranking battery (Interstate). In a long process not to be described here, I eventually discovered a hard-to-find, intermittent weak ground connection that was probably the source of the problem. Yes, yes, I should have load tested the start battery first. But let's not dwell on my ineptitude. There are others in my household to help with that.

So I have this extra one year old battery that is perfectly good and was thinking about adding it to the house battery bank so I can be an amp hog on the hook. I already have a switch that allows me to parallel the house and thruster, so this is icing on the amp cake. After $20 for a battery box and another $20+ for cables, and the requirement to buy a fifth battery when it comes time for a total swap, I am having false economy and sunk cost effect discussions with myself. Still, these boats are all about being comfortable and secure, and this is small change compared to filling the tank.

For those who have rationalized adding an extra battery in their R-27, where did you put it and did you run into any charging problems?

 

[knotflying]

The ground on my boat to the engine passes through 5 connections before it gets to the engine block. I left the existing ground and purchased additional cable and connectors and ran a ground straight from the engine battery to the block. A cost of $50.00, but some comfort in redundancy.
On a similar note, everyone should make sure that the connections going to the ECU are clean and free of corrosion. In talking to Yanmar about another issue, I was told that there can be erroneous error messages etc. if the connections are poor.

 

[wincrasher]

Our boats would do very well with Lithium (LiFEPo4) batteries. A group 31 battery only weighs 26 lbs. An expensive project, but would probably solve the port listing issue.

 

[Sam Walker]

Hi Hydraulic. If I have read your post correctly, it appears that you are planning to connect the existing deep cycle house battery with your now surplus starting battery to make two batteries for the house? If so, this is not a good idea. The unlike batteries will not be compatible in the ways they draw down and recharge. It will ultimately lead to killing both batteries prematurely and you will likely not get the amount of draw down that you are expecting when on the hook.

 

[knotflying]

Sam, I may agree with you, but with the relays ultimately connecting all the batteries at various charge stages how does your point hold up under that scenario?

 

[Hydraulicjump]

Thanks Sam. And no, the battery I would be linking to the house batteries is an identical, same age deep cycle marine battery. It was being used as a start battery when I accused it of being weak and replaced it with a cranking battery. It was falsely accused. The culprit was an intermittent weak ground.

 

[Sam Walker]

Excellent, Hydraulic. You should have no worries then.

Knot, since I don't own a boat w/ the set up that Hydraulic's boat has, I cannot comment specifically to what part relays would play. However, the ways that starter batteries and deep cycle batteries are made internally are different. Deep cycle batteries have thicker plates. This allows for the amperage and voltage to drop down differently as they are being used and discharged. This results in the different types of batteries wanting to be at different voltages. Since differing voltages are not easily achieved when the batteries are connected to each other, the batteries take on a subtle battle to determine which voltage will win. This the battle can have the effect of killing one battery faster than it normally would. It also causes problems when charging, which will lead to false or incomplete charging of one or more batteries. Generally, a starter type battery will charge (and discharge) faster. Thus, the charger may see the higher voltage and shut down the charge too early for the deep cycle. This voltage issue can even exist in two similar batteries of different age. The rule of thumb is that when one battery of a bank goes bad, one should replace all in that bank. YMMV.

As stated already, this would not appear to be an issue now that Hydraulic has clarified both batteries to be same age and both deep cycle.

Sam

 

[Hydraulicjump]

End to this short story/post. I bought a $15 Group 27 battery box and fit the extra battery very nicely next to the propane tank beneath the lift up seat in the rear of the cockpit. For those of you with younger R-27's, you have your propane in a box on the swim step, but we old timers have the higher risk propane box beneath the rear seat. Regardless, easy to have two cables linking this battery in parallel to the thruster battery. Thanks to advice on this site (and as noted previously) I have a switch to parallel the thruster and house batteries. Everything charged fine (I checked all batteries and there are no weak ones) and all worked swimmingly today with lots of tests. Next summer, when we are at week two of three in Desolation Sound and our portable 12v freezer is stocked full of vacuum-sealed fresh caught Chinook and coho (and maybe some ice cream?), I can rely on my massive 4-battery house bank to avoid defrosting disaster overnight.

Of course, "rely" is conceptual. This concept has not been tested and my fishing success is, at best, stochastic. Will report back on the former, but most certainly not the latter.