I have had difficulty finding a battery that will start my 1992 XJS V12. I wanted to go to a yellow top Optima for the high cranking current and deep draw capability but Optima does not say that any of their batteries fit this car.

I now can confirm that an Optima Yellow Top 3478DT fits very nicely. The top holder plate fits the top of this battery nicely. I needed to buy longer bolts and modify the shape of one of the hooks but that was easy. The car starts great with this battery.

 

I have one for my 84 XJS, and your right about the fitment

 

what about vents? and piping for them?

 

It's a sealed battery - no vents needed

 

Interesting! I have a '93 Coupe with a standard no maintenance Interstate battery. The car was purchased used and had four trunk floor vent holds open. Is that the proper way to vent the battery or did Jag enclude a vent system? Currently the trunk shows no deterioration or rust.

 

regular batteries vent Gasses (hydrogen) it is very flammable... that is why the piping to the battery vents,

Opitma batteries do not expel gasses unless they are over charged... so you are good to go with one... and they are sealed and do not spill

 

From the factory, the XJS battery had a vent hose connected to it. The hose exited from a small hole in the bottom of the passenger side rear fender.




The four holes in the trunk floor are there to allow drainage as needed during the manufacturing process or for service operations. They are not meant to be open all of the time. When the car was originally built all of the holes were fitted with rubber plugs.

Mark

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Thanks Mark, I am not sure, from your drawing which part is the vent hose; perhaps 3?
Is 1 a cover to trap the gas? Without these parts I am not sure how to vent my battery. These may sound like dumb questions, but I have not seen an XJS except the one I own

 

Part #1 is the battery. Parts #2 and 3 are the vent hose and elbow. The original battery was a non-sealed type and had a vent built into it's top to which the elbow and tube connected. The tube then ran out a small hole in the fender and exited under the car.

Many new batteries (non-sealed type) still have provisions for a vent but it may not be located on the correct side of the battery. In that case you would have to run a short extension hose and join it with the original vent hose.

Of course many batteries now are the sealed type and not vented so you can use one of those and not worry about connecting the hose.

 

Got it! Non sealed run a vent hose; sealed no vent hose. Since I have to buy a battery, the sealed one will be my choice.
The previous owner left the four floor hole open, I suppose, to vent the trunk. It seemed to work as the trunk is clear of any corrosion or rust
Thanks for all the info...it was appreciated

 

I would ask your retailer but most new batteries today are sealed...

 

I told my wife I was no longer going to buy automotive car batteries...
no not ever... again...

no acid, no fluid, no gasses, weights just a few pound... 16.7volt rating
Boost cap module 12X 350 farad caps 12V 600CCA starting current
189.00 us $

or you can just go crazy and use 6 x 3000F 2.7 volt Super caps \giving 500F at 16.7 volts cost more though...

this is what I am going to put in my XJS (the 189.00 one...)

these are available on ebay... and there are videos on utube how to build your own... one nice guy built a 350F x 6. starts his car nicely ,but he wanted to listen to his radio with the car off... (not so good for that) he made his into a hybyrd by adding a small large capacity rechargeable battery in parallel ( he also learn not to use it to jump another car because it toasted the rechargeable, needed to add a circuit to keep the rechargeable from completely discharging or a switch to disconnect it while jumping some one )

going to save me a bunch of weight...

 

My interstate battery barely fits. It has a little lip I had to shave down a bit. Nothing remarkable about it though, I think it has lower CCA than the one in the land rover. I don't like thinking about it because it should be bad by now....

 

Copied this from the Optima site.
Find a Battery | OPTIMABATTERIES

Trunk/interior mounting – If your battery is mounted inside the passenger compartment or trunk (common in many European makes), the battery must be vented to the outside of the vehicle. OPTIMA® group 27, 51, DS46B24R, 78, 34C and 31 batteries all have ports for connecting a vent hose.

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More info for 1993 XJS
Your Battery Results*
1. Group Size: Minimum Cold Cranking Amps: · H5 · 590
*Confirm these recommendations with your local battery retailer to ensure proper fitment.
H5 in Inches (L x W x H): 9.56 x 6.88 x 7.5 (From Walmart site)
Qptima Red group BCI 25 and 35 have close matching dimensions, cci 760, Ability to vent not known

 

I bought a Continental vented battery from Standard Parts. Relatively inexpensive at $87.00. I will not instal it until I take action to remove any sulfuric acid residue. Altho I show no deteriation from my current non-vented battery, I intend to remove all carpeting, battery and spare tire.and spray the trunk area and other visual points with a solution of bicarbonate of soda and water. This should kill any residual sulfuric acid. I will do the same with the carpeting and tire. and then flush everything with water. If there is any visual rust i will spray it with rust killing paint. The whole operation should cost less than ten dollars and a couple of hours labor.

 

Maybe this is why you should consider venting your battery!
DIY hydrogen generator

 

Just adding to this old thread because it was helpful to me this week.

The Optima YellowTop 34/78DT in this thread also works in my 1990 XJS Convertible.

The terminals are farther back in position (closer to gas tank oppose to say tail of car), so you may have to undo some zip ties or cable ties to give more slack to the positive and negative cables. The fit is snug in the tray, but definitely a fit. The top holder fits just as snugly, but also definitely within the realm of proper fit.

Thank you to the original poster for sharing this info because the Optima website does not list this as a fit for our XJS cars. My guess is that their database didn't bother to test fitment for the XJS given the low number of cars out there in the world.

 

I folded a McDonald's paper bag into the battery to get simple portable measurements. Then I went to a battery store, plopped a red Optima battery ontop of the bag and knew that it would fit. Just the poles needed a little cable tucking.