Fitting mobility 12volt AGM battery.

Next weekend I shall be fitting a 60amp/hr 12volt mobility battery to a friends Prius. I will take pictures of the procedure and give fitting details for those with interest.

John (Britprius)

 

I think this is a difference in terminology between the US and Europe. Had a similar discussion in an early post.

John (Britprius)

 

I wish batteries did behave this way, unfortunately the rate of discharge greatly affects the capacity of the battery. Most manufactures of lead acid batteries rate them at a 20 hour rate however the batteries I am installing are rated at a ten hour rate of 55 amps. Aligning them with other manufactures that rate there products at 20 hour rate means the battery is actually rated at over 60 amps.

John (Britprius)

 

For those that doubt the advisability of fitting an AGM mobility battery in a Prius I ask them to read this with an open mind. If you have any concerns please raise them and I will attempt to allay any fears, but I make no apology for information from any previous posts repeated here as I wish to put all the information in one place.

The reasons for fitting a mobility battery are not at first obvious, but they are generally of rugged construction, high capacity, and second to non at being able to withstand deep discharge the very reason for there use in mobility scooters and wheel chairs. They are also very safe another requirement if your sitting on top of a couple, and used indoors.

For use in a Prius these advantages can be fully utilized. The OEM battery although an AGM doe not stand up well to being discharged, it's capacity is between 35 and 40 amp/hrs depending on the model of car. The maximum discharge level most battery manufacturers recommend for longevity is 50% of capacity and this is considered deep discharge.

Mobility batteries are used in continuous deep discharge situations often being discharged and charged on a day by day basis and are often rated to 80% discharge and well over 1000 cycles. Of course the lower the number of these cycles and the reduction in depth of discharge greatly enhances there life span to the point being in standby use " being used only rarely and float charged to keep the battery fully charged" there expected life span is as high as 18 years.

So a 60 amp/hr mobility battery can have 48 amp/hrs of capacity removed before it reaches it's deep discharge level, and recovers from this without problems. these batteries in fact do recover well from complete discharge. The larger of the two sizes of OEM batteries fitted in the Prius used to 50% of it's capacity the maximum discharge level recommended for deep discharge can output only 20 amp/hrs and even then does not recover well. This translates into the mobility battery being able withstand much longer periods of non use of the car and recover better from the discharge of the battery in this situation.

The battery I am fitting in a friends car is a 55 amp/hr battery "at 10 hr rate" made by Ritar part number
RA12-55 the same as fitted in my own vehicle. (This is not the only battery recommended "see list at end of post" but one that is available to me localy) It's voltage not out of it's box was 13.0 volts as shown in picture (1) measured with two different DVM's. I advise buying batteries from "if possible" direct from companies that have a large turnover of batteries and sell little else.

It measures in mm:-
229 long, 138 width, 210 high.
In inches:- 9 long, 5.4 width, 8.27 high.
Weight is 18kg or 39.6 lbs. This is probably the only downside against the OEM 11kg or 24.2 lbs, but the capacity of a lead acid battery is directly related to how much lead the battery contains.
This puts it's physical size as being very similar as the larger of the two batteries fitted in the Prius in the US with the larger battery tray, and the same size as the UK/EU versions. Comparison picture (2)

It is a valve regulated lead acid absorbed glass matt battery (VRLA), (AGM) with external vent as is the OEM battery.
Maximum charge rate (before gassing) is 16.5 amps, as against 4 amps for the OEM. It is a pity the maximum charge rate in the Prius is so low "4 amps" as if the system could charge at 8 or 10 amps recovery from a low state of charge battery would be much quicker helping to protect the battery from damage, but this rate of charge was obviously chosen for the maximum charge rate of 4 amps of the OEM battery.
Maximum discharge rate is:- 1000 amps for 3 seconds then 550 amps.
Self discharge rate is less than 3% a month.

The big differences between this battery and the OEM is it's capacity and it,s ability to withstand deep discharge without damage.

It,s capacity if measured at a 20 hour rate (that of the OEM and most other lead acid batteries including the Optima) is over 60 amp/hrs or 150% of the larger of the two OEM batteries. The battery may also be used in any orientation including upside down without problems.

There is also a gel version for those that wish to be supper safe with no liquid acid at all, although it's maximum charge and discharge rates are slightly lower, capacity remains the same, and should not affect operation in the Prius, but the gel version is not recommended in very cold climates.

This makes it ideal for those that on occasions do not use the car for extended periods "left at airport ect", are using high power audio equipment, or are using high current inverters from the Prius 12 volt system.

Ritar rate the discharge capability of this battery as 1200 cycles down to 80% of it's capacity, that would be the equivalent deep discharging and charging it every day for over 3 years and 3 months. It also may be discharged completely without problems.

For standby use on float charge at 25 degrees c it's expected life span is given as 18 years. It is shock and vibration resistant as is to be expected because of it's possible use in electric wheel chairs and mobility scooters with no suspension. It can be used in cyclic or standby use (float charged)

For those that wish to stay with the original capacity battery with smaller dimensions (fits the smaller battery tray) use the Ritar RA12-33 or equivalent at around £45 or $65 (1/4 of the similar rated Optima in the UK and half the cost of the OEM) still retains the attributes of the larger battery.
Sizes in mm:- 195 long, 130 width, 167 high. In inches:- 7.7 long, 5.1 width, 6.6 high.

The cost of the battery in the UK is less than the OEM by a substantial margin, and well less than half the price of the Optima. I believe in the US similar batteries are available for around $100 but according to the Ritar web site they are sold in the US. I will add a list of manufactures that make batteries of this size and the smaller battery available in the UK and else ware at the bottom of this post, not all are made in the UK.

Ok first thing is to strip out the rear floor panel, battery cover, and rear cargo under tray, then remove the exhaust air vent tube from the HV battery.
Then remove the negative battery wire where it is bolted to the rear panel. Next disconnect the positive battery clamp and lift off. Remove the battery hold down bracket and battery vent tube then lift the OEM battery out of the car.

Next there are a number of options for connecting the new battery as it's terminals as it comes out of the box are 6mm vertical bolts supplied with the battery. The terminals are in the same orientation as the OEM battery.
These options are shown in the pictures with the battery not in it's operational position for clarity purposes, and the options are in no particular order of merit.

(1) The first option is to use screw in JIS adapter posts that can be purchased at good battery stockists, and then everything goes back together as the OEM fitting, but my friend forgot to purchase these when ordering the battery so cannot be shown. These can however be made very simply by following the instructions in option (4)

(2) The second option is to fasten the Prius clamps down with the bolts supplied with a suitable washer on the top and a nut (or suitable piece of tubing) fitted inside each clamp to keep the clamp concentric with the post.

(3) Third option and the one used is to remove the positive C clamp by removing the single bolt holding it, and using the hole left in the terminal bolt this down direct to the battery. See picture (3 and 4 ).

The negative can be fastened as option (2) or the cable from the battery can be replaced by one with terminal eyes on both ends, (scrounged from a breakers yard). Or the method used by myself the C clamp bolt is removed the terminal laid on it's side and the new bolt supplied fastening it down to the battery, this make a very secure fixing. See picture (5) The terminal when fitted should be turned 90 degrees compared with the picture so that the cable runs along the top of the battery (makes fitting the battery easy).

(4) The fourth option is to drill a 1/4 inch hole down the center of the old OEM battery posts to the depth of the top of the battery, then the posts are cut off with a hack saw close to the top of the battery case. "Lead is very soft drills, and cuts very quickly and easily". These can then be bolted to the top of the new battery making sure you have them in the correct order, the larger one being positive + red. The battery can then be fitted as normal using the existing fittings.

Whatever method is used it is suggested that any parts that are removed and not used are packed in a piece of sponge inside a zip type plastic bag and placed by the side of the battery in the car. If at any time the car is required to be fitted with an OEM battery all the parts are at hand and in good condition.

Some total of parts not used. Picture(6)


When fitting the battery in it's tray slide it back towards the rear of the car before clamping down with the OEM clamp. The only modification here was to use a bolt 1/4 inch longer than the OEM for the fixing clamp between the battery and the capacitor block (black plastic box next to battery) everything else fits fine.

Suitable batteries are made by these manufacturers and are available in the UK. Most of these are not manufactured in the UK and many should be available in other countries including the US and Canada. Search for "mobility batteries", below is a list of manufacturers batteries being sold in the UK but this is not an exhaustive list. Note the Ritar battery is an US company as shown on the battery (not made in the US).

Lucas, Haze, Ritar, Platinum, MK, Long, Ultra max, T-Power, Leoch, Sterling, CSB, Remco, Genisis, Yu-Power, Fulriver, Yuasa, Matrix, Strident, Electroquest, Powersonic.

Some manufacturers make the same size batteries with bolt through lugs above the surface of the battery. These batteries will work just as well. All that is required is a little thought in the method of connection, the physical sizes remain the same.

Finally voltage readings on the MFD. Picture (7) with start button pressed once "no brake" 13 volts.

Then with the button pushed twice "no brake" with headlamps on. Picture (8) 12.8 volts.

I hope I have left nothing out and I will be happy to answer questions.

John (britprius)

 

Ritar is according to the information on the side of the battery is a US company but the battery is not made there. There UK web site intimates that the battery is sold world wide including the US.

 

Yes the battery is vented in the same position as the OEM, Thanks for bringing that up something I omitted in the wright up.

The Prius angle tube fitting is to large and also the rubber tube is a little loose on the Ritar battery but I found screen wash tubing (2 inches) fits the battery and pushes into the Prius rubber tube nicely. I have had one fitted in my own Prius for about a year now.

I also have a mobility scooter with two of these fitted for over two years " deep discharged and charged every day" without problems.

John (Britprius)

 

Yes that is the same sort of capacity as the OEM battery. It is not quite as tall as the OEM so would need a wood block underneath about 1.25 inches thick.

John (Britprius)

 

The only downside that I am aware of is it's extra weight Some 15 lbs, but the only analogy I can think of is it's like carrying extra fuel in a larger tank. A lot of people have more weight than this in junk in there cars.

John (Britprius)

 

The only history I have got is one year in my Prius, and use in my mobility scooter "2 years, two batteries 24 volt system". My sister uses a wheel chair permanently and has had two in that for 5 years again a 24 volt system. Deep discharged and charged on a day by day basis.

John (Britprius)