Replacing Battery

[mmdesmith]

My 5 year old battery finally failed in the Texas heat. I am going to upgrade the engine battery to 115 amp hours. I will also look to replace the house battery as well. Both are deep cycle batteries.

I have always kept both batteries "On". Does anyone turn off the engine battery to preserve for starting purposes while sailing?

I have seen a couple of posts regarding not turning a battery off when the engine is running to protect the alternator. I am assuming this is okay as long as BOTH are not turned off.

 

[Ron20324]

My B323 has three batteries. I leave them on all day to charge via engine or solars, but always shut one off at night to be sure I have engine-starting ability. As long as you have one battery connected to the alternator, you can turn the other one on/off.

 

[Gunni]

Check your wiring diagram. My batteries have a jumper wire that feeds alternator charge to the batteries even if the load side is off. But yes, I always leave my engine battery in the off position for emergency start use.

 

[Tejas]

We're on Lake Travis in Texas and in September will have eight years on the original batteries. We leave both batteries on when sailing and off when in the slip. We have a battery combiner which if I understand correctly, combines the starting and house battery for starting and otherwise isolates the starter battery.

Because of the drought, we can no longer rely upon shore power for charging the batteries and instead rely upon a small solar panel. Although when the batteries are off, there is still a .1 amp draw, and that is why we need solar to maintain a charge. The reason for the draw seems primarily to be paradoxically from the battery monitor. There also seems to be a low draw from a Sony AM/FM radio, apparently the purpose being to preserve radio presets.

The batteries are AGM and before installing the solar panel two years ago, the .1 amp draw depleted the batteries, and I thought the batteries were dead. However, taking the batteries home, charging the batteries for several days with an automotive battery charger recovered them.

 

[Philip_Oceanis 361]

If your batteries are completely separate (like in my B361) it doesn't really matter whether the engine battery is on or off when the engine is off (saying this I turn it off at anchor just in case....plus I have an extra switch to connect it in parallel with the house batteries again just in case).

PS: Why do you need such a big battery (115amp) for the engine anyway? Most probably what is needed is around 70amp and unless you plan to use it for house purposes too I cannot see any advantages.