Seems a battery that will fit the XJS and has the right dimensions, sufficient CCA, and has a vent port is hard to come by now. The red top 35 has the positive post on the right and will fit in the tray but is not vented.

Exide stopped making the vented replacement. Very few batteries with the positive on the right and none that seem to have a vent post because this battery sits in the trunk you need it vented. I am stumped at which battery would work. The ones recommended at Walmart, optima etc don't fit in the tray and have the wrong post configuration.

Any advice would be greatly appreciated.

 

I picked up the above for my 96 4.0 XJS and its been working for me without problems. I'm not sure if the dimensions for the battery tray ever changed so would be best to check the product dimensions.

 

I purchased a new battery this year from uk seller euro car parts and they list for a v12 a larger 9 plate battery which doesn't fit without a bit of tin bending and welding of the fixings but with a massive 60% off and a lot of electrical upgrade on the car I thought it was worth the effort.. As far as venting is concerned never been vented since I purchase the car 25 years ago, never been an issue.

 

I don’t want to derail the OP’s topic (sorry OP) but I am confused every time I hear about “vented” batteries for the XJS.....aren’t almost all batteries sealed now? What are they going to be venting?? As far as I know, Optima batteries are all sealed, and they will not vent or leak acid........why would you actually want a battery that is not sealed and vents? Just to use the vent tube in the car?

Not being snarky here, I am just wondering....I just replaced the old Redtop Optima in my car with an identical one.

 

It is a good question and a miss understanding that is held by many. I checked directly with Optima and they said that we should not use an Optima Battery in the trunk of our Cars that is not vented. Is is a miss conception that the Optima Battery is sealed. It is not sealed. It has two self sealing vents which are those black circles on the top of the battery. But when overcharged those dump explosive gas into the trunk of the vehicle. The only Optima batteries that contain vent ports are the following, and this list came directly from Optima,: 27, 51, DS46B24R, 78, 34C, 31 and H6 and none of those batteries will fit properly or have the right Cold Cranking Amps for our vehicle.

Here is the direct quote from Optima and this would apply to all AGM and Gel Batteries:
Thank you for your interest in Optima Batteries. It is important that ANY lead acid battery has proper ventilation. ALL lead acid batteries can vent gas. Traditional wet batteries do this immediately when recharged since they are not sealed.
Sealed lead acid batteries like Optima and all other “Dry Cell” batteries have safety release valves that will only vent if they are seriously overcharged. Under normal operating conditions an Optima will not vent gas.
Since alternators or chargers can fail, the safest and correct mounting method for trunks and passenger compartments is to make sure that any possible gas venting will escape to the outside of the vehicle. All vehicles with original equipment battery locations in trunks or passenger compartments will have a vent provision that should be used. If you are custom mounting a battery in the trunk or passenger compartment we recommend venting the battery to the outside of the vehicle also.

If you installed a regular red top Optima Battery in your car that does not hook directly to your vent hose or is not isolated in a vent box that hooks to a vent hose then you are essentially riding around in your own potentially explosive death trap. Also, you have the potential of seriously damaging your car with vented gas from overcharging.

 

 

That is a good one. I have personally experienced a battery overcharge that resulted in an explosion of the battery. It was not an optima battery and it was not in my XJS. But, it did make a mess in my engine compartment and I used up a lot of baking soda. The engine compartment is a lot more vented than the trunk of your car and it still exploded. So, you have to determine if you feel like gambling. If you like gambling that your charger and your alternator will never fail and will never overcharge your battery then using a normal Optima Battery or AGM battery without venting might be the thing for you.

That is why it is so challenging to find the right batteries for our cars now, because we need to properly vent even the so called "sealed" batteries.

 

Just my opinion -

if the battery can explode under the bonnet which is very well vented, then what chance that the two vent lines leading from the battery to the outside of the boot/trunk can get rid of the hydrogen/oxygen quick enough to prevent a similar explosion?

I presently have my spare VE Commodore battery in mine when required which has the venting capability, but has the terminals around the wrong way - fortunately my leads can go either way (They can be closer to the fuel tank). (The VE has the battery in the boot area as well).

Below is from a commodore forum (I think these were sold as Chevy's in the States). Which is a pretty good read for the issue and has a bit of Aussie humour

https://forums.justcommodores.com.au...y-vent.277674/

I will be installing a vented battery when she is on the road - not for the explosion side of things, but for the corrosion side of things. During the rust removal process, directly above the battery had the dreaded bubbles

Cheers
Steve

 

Yes, That commodore forum says the same thing we need to vent the battery. Thanks for sharing that. Now If I can just find the right battery, that fits, can be vented and has the right cold cranking amps and is available now.

 

Thanks for your reply.

I do hope I am not running around in a death trap! My red tops are usually connected to an Optima battery charger I purchased concurrent with the battery.

On the Optima website, they have the Yellowtop H6 as the battery they recommend for a 95 XJS such as mine. Looks like it’s vented and it does have the correct cca. I will have to measure the tray tomorrow to see if it will actually fit.

There are many topics here of people using non-vented Optima batteries I have never heard of anything ominous happening, however that does not mean that what you stated is untrue. I am now certainly concerned and will continue to research this.

thanks

 

I have a group 47 in my facelift car and it works well. I don't know if the battery tray changed between facelift and pre facelift cars.

 

I guess I could use that battery if I replace the battery tray. The tray in the 88 XJS is only 10" x 7". Maybe that will be the easiest path to take. That is, fabricate a new battery tray that holds a larger battery that can be vented.

 

.................you are not helping you know that dont you

But i cannot help but think;

How many older high end cars have there battery's in the boot. Many.
How many of those are now just drivers being driven into the ground as daily drivers. Many
How many of these have the right battery..............or just a budget battery that fits and has the correct cranking amps. Many
How many boot explosions ive heard of as a result, one, now.

Given how much water finds it way into my boot im not that worried about ventilation

Just sayin

 

I guess having lots of holes in your trunk is one form of ventilation. Here is some info. Hopefully this will never happen to anyone reading these:

https://www.latimes.com/archives/la-...902-story.html
https://www.aswllp.com/Results/Autom...ttlement.shtml
https://www.yachtingmonthly.com/arch...-avoid-it-3930
https://appel.nasa.gov/2018/06/25/sp...ery-explosion/
http://www.theaic.org/pub_thechemist...Article-4.html

Better safe then sorry, Please vent your battery and pick one that can be vented if your battery is in the trunk.

 

That should fit a group 47 battery. Spec on those is 9.7" long and 6.9" wide

 

This is a photo of my modified battery box. The original cover and sump guard was long gone before it became mine

The brown wire is just temporary at this time (getting power from the battery to the relay.

 

Thanks for this thread. The PO of my 87 had installed a Delco 34PS battery that has been working just fine so I didn't give it a second thought. On inspection though there are no vent hoses attached, or present. I'll try to figure out what fits. If anyone has insight into the correct vent hoses that attach to this battery it would be much appreciated. Getting from there to the boot floor I can deal with easily..just the battery connection...for some reason there's no vent kit-to-battery cross reference from Delco