AGM Starter Battery - Jag V12

[101RRS]

The previous owner of my Jag XJ 5.3C installed an aftermarket ECU where the battery would normally sit in the engine bay and moved the battery to the boot.

In their wisdom they installed a Odyssey AGM 25- PC 1400 battery - it has a 65Ah capacity and 880CCA. The battery is only 2 years old, and only travelled about 10000km.

Recently, the battery has started to lose charge and failed to start the car on two occasions though it will turn the engine over. The obvious place to start looking is to see if there is a parasitic drain and if there is - the aftermarket alarm/immobilizer is the first place to look. How do i measure if there is a drain on the battery with everything turned off.

The other place to look is the alternator which was rebuilt along with its regulator about 3 years ago. There is little output at idle (800RPM) but it soon moves up into the normal range on the dash voltmeter with a few revs. The gauge shows normal but on the low side and the charging light is off - any tips on checking this?

Lastly, how do I check whether the AGM battery is healthy and is not the problem? I have never had an AGM before. If the AGM is at fault should I change to a standard starter battery - the AGM currently lists at around $650 where a normal starter is about $300.

Thanks

Garry

[RANDLOVER]

You can use something like this DC Clip on ammeter ToolPRO AC/DC Digital Clamp Meter 400A & 600V | Supercheap Auto (https://www.supercheapauto.com.au/p/toolpro-toolpro-ac-dc-digital-clamp-meter-400a-600v/636959.html?gad_source=1&gclid=EAIaIQobChMIgNnB6ZSZgwMVddsWBR2EjgsfEAQYASAB EgIVtvD_BwE&gclsrc=aw.ds) or put an ammeter in series by disconnecting the battery and putting the leads between the battery post and and battery terminal, starting on the highest scale as you don't want to pop the ammeter with over current.

[101RRS]

With the car sitting the battery goes down to 11.5v over about 5 days but is still able to start the car.

Charged the battery over night and disconnected it from the charger this morning - while on charge shows 13.4v and when disconnected goes straight to12.7v - by mid afternoon it had dropped to 11.3v and while it will crank a bit, it will not start the car.

So it would seem that the nice and expensive AGM battery has died after just 2 years. I have a nice big RRS battery that is spare that would suit the Jag very nicely but it is physically too big to fit.

So the decision is whether to get another AGM of the same size Odyessy or just go for a standard starter battery.

Definitely not paying $650 for another Odyessy.

Garry

[Graeme]

A battery in the boot can't be a flooded wet cell unless it has an external breather fitted, so another AGM is likely required.

[LuckyLes]

Check the warranty on the battery, I think they are 3 years for private use.

[101RRS]

A battery in the boot can't be a flooded wet cell unless it has an external breather fitted, so another AGM is likely required.

Oh OK - had not thought of that. Technically the boot is ventilated as air from the cabin goes into the boot and then out through vents in the rear boot floor - but yes is something to consider.

Thanks

Garry

[101RRS]

Check the warranty on the battery, I think they are 3 years for private use.

Yes thought of that - battery was bought by the previous owner interstate - will probably be too much hassle to claim but will look into it.

Thanks

Garry

[oka374]

there are lots of vehicle fitted with wet cell batteries internally, our XC70 Volvo wagon has the battery iunder the boot floor beside the spare wheel, it is a normal wet cell and has a tube running from the vent on the battery out through the floor so is sealed from the cabin.
The sons BMW X5 also has a huge wet cell battery under the rear floor with the same setup.