Installed higher capacity AGM battery in third gen RX450h

[Barry14UK]

As many are only too well aware, the 12v VRLA AGM original Panasonic Battery in the third generation is only rated at 51Ah and unless it is regularly charged by one of several ways, it can go flat quite soon, particularly as the Battery ages. So the risk of a flat Battery increases at

airport car parks for extended times for example. Certainly, there are ways to get the traction Battery to work in an emergency but the fact that the 12v Battery has been allowed to drop below a critical level means it's life will have been shortened. I therefore did a lot of research to find an AGM Battery to upgrade the original one. (There are a number of free flow lead acid batteries that could be accommodated within the Battery compartment under the rear hatch but I excluded these as I wanted to fit an AGM type like the original).

I wanted a Battery that met the following criteria:-

It would significantly increase the Ah over the original Panasonic one.

It would be less expensive than an original replacement, be widely available and have a long warranty.

It would not be necessary to cut the actual Battery compartment to install.

It would be easy to remove the Battery and fitted components so the next owner could return to stock if wanted.

All of the above was achieved by simple changes to fit the 027 60Ah AGM Battery, a size that is available from leading makes. I opted for the Halfords (Yuasa) one, using my Gold Membership 15% discount, as it provided a 5 year warranty. Furthermore, should the Battery fail prematurely, there are many branches where it could be exchanged. It was necessary to jack up this Battery to help clear the sloping sides of the Battery compartment and also to pack each side at the top where the angle of the retaining strap secures it each side. This is critical as there is a correlation between the top and bottom packing and each must be right. You then need a way to get the existing earth strap back over the hump of the Battery to its original fixing point. I achieved this by using an auxiliary terminal clamp onto which I screwed a brass post. (I could have used an after market earthing strap with a different end but wanted to retain the Lexus one).

So the above are the bits I needed. I tried to make the packing parts complement the original as far as possible by making them out of black polypropylene. I cut the Battery tray and let in 8mm of polypropylene to extend it. I must say that I have fused other plastics together fairly easily in the past but found polypropylene is a very difficult material to work with and I would not use it again! I would just omit the tray as it serves no useful purpose with an AGM Battery. (I note that on some USA forums members have just cut the ends of each propylene tray and extended the tray by flattening the lip). The advantage with my extended tray is that if an owner reverted to an original Battery, it would look very near stock. Even with the extended Battery tray I had to alter the angle of the projection at each end using heat in order accommodate the Battery clamping extensions. It would have made it easier to cut off these clamping extensions on the Battery as they are just in the way, but would doubtless have invalidated the warranty should I have to claim on it.

It would have been a lot easier to have made the two packing pieces that go beneath the Battery retainer at the top out of wood. The bottom packer could be made of plywood, sloped in at the bottom, best used without the original plastic tray or with the lip at both ends of the tray let down.

Cost of project in round figures.

Halfords (Yuasa ) 027 AGM Battery on offer with discount from local branch £103

Neg earth clamp and pair of brass terminal posts with allen screws , only neg used £ 20

Polypropylene for base and top packer £ 7

Milliput as core for top packers to prevent crushing £ 5

Vent elbow £ 6

Polypropylene DPC used 1 layer below tray and 1 above £ 0*

C.T.1 Adhesive/filler thin layer between DPC and tray to take out welding unevenness £ 0*

Swear box , should have been more!! £ 1

£142

*Had some of this from another job and not necessary if wood is used instead of

polypropylene

Well here are some pics showing parts I made/purchased before and after assembly. NB. I did find I had to reduce the length of the top packer on one side as it came up to the Red cover of the positive terminal. I also had to replace the vent tube elbow with a more standard size as the Panasonic one has a larger port. Finally, I had to further relieve the cut away in the compartment cover slightly to allow for the longer Battery.

If anybody else wishes to do this, feel free to ask any questions including where I sourced the brass post and auxiliary negative earth clamp, the only one I could find that was threaded to take the 8mm Allen stainless screw for the brass post – they are usually 10mm. Hopefully, from the narration and pictures below this should made it clear.

1st Picture - with compartment cover in place

2nd Picture - Parts used less vent elbow

3rd Picture – Installed, and to borrow an Allen Millyard expression ,“It fitted perfect”

 

[Illogan]

Excellent job Barry - - and sincere thanks for sharing!

[Barry14UK]

I have very recently learnt from another member that Yuasa has now introduced a new AGM Battery ref HJ-S5523L* with the same dimensions as the Panasonic fitted to the later series before the 4h gen RX 450h.  This Yuasa Battery is rated 57Ah against the 51Ah of the Panasonic original and should be a plug and play replacement.  However, it is expensive at around £250 delivered and the one seller I could find stating a warranty, gave this as only one year.  So if needed at short notice away from a closed Lexus dealer, it could be an alternative.  

However, this Battery, which  Yuasa label as 'Auxiliary', is double the price of the one I fitted but has slightly lower Ah rating and is significantly  lighter, so likely contains less lead.  The 60Ah Halfords (Yuasa) I fitted also has a 5 year rather than a 1 year warranty and is made by many others using the much more common 027 casing.

So if you want to keep to an AGM Battery as originally fitted, you now have the options of an original Panasonic, the Yuasa as above, or the 027 with light adaptions.  Alternatively, if you are happy to replace with a flooded lead acid Battery as some members have done, these can be bought at less cost and are more readily available in a suitable size.

*If opting for this ensure you get the one with suffix 'L' as this Battery has also been released with the same reference but with the suffix 'R', denoting that the + and - terminals are transposed.

[MUDGUTS]

My car had a replacement Battery fitted before I bought it. A 60 Ah. Priced about £65. Interested in opinions on whether it would be worth upgrading this. 
 

[Barry14UK]

That looks like the Battery Varta suggest for the model although it is not an AGM one but is a type a number of people have fitted apparently without problem. One advantage of an AGM type is that the acid is contained in the glass mat and not loose, so in the event of a crash there is less risk of occupants being affected by the acid.  However, this risk is very small and indeed Lexus have not fitted this to some other models.  There has been some debate on how much better the system works with AGM  type where originally fitted but owners have not reported any significant difference when replaced with a free flow type..