Battery in the engine bay?

[Sailorman Ed]

I know that heat is the enemy of batteries and mine came with the batteries mounted above the engine (each hull). (please ignore my temp wires - large rewire project in progress) Currently the positive lead goes forward about 6 feet to a disconnect switch and then back 7 feet to the starter (Yanmar 2GM) - about 13 feet total.
I am soon to replace both start batteries and thinking to move them forward OUT of the engine bay. I have 2 choices:

1. there is barely enough room under the aft berth next to the diesel tank to fit a start battery but a real hassle to gain access to check water for a normal FLA. Battery venting issue also.
2. move it a bit farther forward to where the shut-off switch is and take away from clothes storage space in the aft cabins. Easier to wire, easier to check the water. Move weight slightly forward.

Worth the trouble? Option #2 a better choice?
Ed

[Cheechako]

I don't think the amount of engine room heat is an issue at all. Internal heat when charging hard is much more of an issue than the ambient space I would think...?
#2 if anything.

[Jaguar2728]

My boat has always had the batteries mounted in the engine room (6 x 6V) The present lead acids have been in for 6 years and still work great, and hold a good charge. I agree with above, its the internal temp that fries them. Make sure you check the acid level on occasion.

[bobnlesley]

It's a non-issue, we too had a boat with the start battery in a very tight/hot engine bay; eight years and never a problem; I would however - even on a catamaran - want the batteries to be strapped down far more securely than yours currently appear to be.

[TurninTurtle]

I'd try to relocate the battery, within the engine compartment, to reduce wire run.

Maybe get it so its not directly above the engine too...

I'm assuming that's a temporary shelf for while you are doing your wire upgrades, not the normal battery mounting. If that's the permanent battery mounting shelf its just wrong.

[Sailorman Ed]

I'm assuming that's a temporary shelf for while you are doing your wire upgrades,

No, that is how it came to me and yes, it is strapped down but you cannot see it in the picture. But I do not like the location, nor the long cable runs.
All the original wire was untinned copper and I have been pulling out unused wire as I find it.

As to temp, I did come across this:
Heat is a killer of all batteries, but high temperatures cannot always be avoided. This is the case with a battery inside a laptop, a starter battery under the hood of a car and stationary batteries in a tin shelter under the hot sun. As a guideline, each 8°C (15°F) rise in temperature cuts the life of a sealed lead acid battery in half. This means that a VRLA battery for stationary applications specified to last for 10 years at 25°C (77°F) would only live 5 years if continuously exposed to 33°C (92°F) and 30 months if kept at a constant desert temperature of 41°C (106°F). Once the battery is damaged by heat, the capacity cannot be restored.

According to the 2010 BCI Failure Mode Study, starter batteries have become more heat-resistant. In the 2000 study, a rise in temperature of 7°C (12°F) affected battery life by roughly one year; in 2010 the heat tolerance has been widened to 12°C (22°F). Other statistics reveal that in 1962, a starter battery lasted 34 months; technical improvements increased the life expectancy in 2000 to 41 months. In 2010, BCI reported an average age of 55 months for starter batteries, with the cooler North attaining 59 months and the warmer South 47 months. Colloquial evidence in 2015 revealed that a battery kept in the trunk of a car lasted one year longer than if positioned in the engine compartment.
I suspect ( will measure temp next time) that it must be well above ambient at the battery shelf after running for a while. I just ordered some fans to direct cooler air to the alternator.

[thomaskoll]

Originally Posted by Sailorman Ed

I know that heat is the enemy of batteries and mine came with the batteries mounted above the engine (each hull).

Air and space are your friends here, the benefit of having lots of space around the battery (that might be charged every day via solar) should eclipse heat danger from running the engines for an hour every few days/weeks.

[pdenton]

I have somewhat the same problem with the engine battery. There's a difference between tolerable, good, and best. I have a 35 foot Pearson with a marinized Kubota. The starting battery is 6 inches from the engine. To remove it is going to require cutting through the galley counter. My Pearson which lacks a quarter birth has 2 huge lockers and a huge lazzaret.

The old house batteries were equally inaccessible and I had to cut and replace with an access hatch.
Whether or not I even triy to remove the engine battery my system is to place the 400 amp hour house batteries and a standard starting batteries in the relatively cooler lockers.

The engine battery and the house batteries will be separated by a Blue Sea automatic charging relay. Please deep-six the One/Two/All mega switches. But do install a high-tech battery monitor.

Without going into the boring details, all distances are available if the wire is the proper gauge. So in your engineering put the batteries, lead/acid BTW, so as to optimize temperature and accessibility.

PHD, PhD

[Mikado]

Regardless of where you put it, it needs to be in a battery box.

[pdenton]

Elementary, my dear Watson.

[01kiwijohn]

You'll be just fine. Longer cable runs require bigger gauge.
Designer s generally consider heat, performance and ventilation ahead of the build.

[SV Sailfish]

Originally Posted by Mikado

Regardless of where you put it, it needs to be in a battery box.

+1

[Reefmagnet]

Own a car? Most batteries are either located beside the engine or in a position that requires longish leads.

[exMaggieDrum]

Battery box if FLA - period. Tie down so even flipping boat won't allow battery to move. If you need to check fluid levels (FLA) you definitely want it to be as easy as possible to check and top off as necessary. If it is hard you will be tempted to put it off and that is death to a FLA battery.

Many, if not most, boats have start batteries in the engine room. The heat is an issue any way you want to talk about it though. Cooler is better. But you also don't want to put a FLA close to anything you value that the gases coming off of the battery can destroy - clothing especially. You also want to make sure it has adequate ventilation, i.e. not tight in a closed in space.