Fitting mobility 12volt AGM battery.

Commenting on an old post, but here goes anyway. That Duracell battery has very large terminals and the bolt used to attach the OEM battery clamp is too long. It isn't shown in any of the pictures but I imagine that half of that terminal and the extra inch (?) of bolt past the nut are hanging out in full view once the red snap on cover is in place (if it can even snap on). The part which on the OEM battery covers the positive post completely. This strikes me as potentially unsafe. There is a very good reason car manufacturers cover up the 12V positive post as thoroughly as possible. While nothing untoward will happen in normal usage, life could get quite exciting if any conducting object happened to contact that exposed metal at the same time it was also in contact with a ground. For instance, a dropped ratchet with an extension and a socket, with the socket landing on the hold down bolt for the clamp.

 

I had some questions about the BLRFM12_55 battery and wrote to the manufacturer ExpertBattery. Their customer service for this was first rate, and they answered all of my questions promptly. However, their last message was interesting enough that I'm going to share it here:

I'm afraid the points they make most likely pertain to many of the batteries discussed in this thread. It doesn't mean these batteries won't work for a while, or even many years, just that they will not work as long as they would in the environment for which they were intended. A UPS battery, for instance, typically spends its entire working life in a (nearly) vibration free and temperature controlled environment. It also doesn't mean that using these alternative batteries will not end up being less expensive than using the pricey Toyota OEM batteries. However, it does suggest "for the best results" vibration resistance should be given considerable weight in battery selection.

The problem with the Prius, at least my Prius, constantly charging the battery at 14.1V (in READY if virtually any "extra" current is used, even Fan speed 1 or turning on the running lights) is discussed here:

Oddity with 12V battery voltage measurements andtranmission | PriusChat

and it turns out several people have discovered this over the years. This issue will affect any installed battery, so it isn't a deciding factor for or against any particular model. However, it implies that since the car is likely to shorten the life of any battery by overcharging it, one might as well use a less expensive battery rather than pay more for a "longer life" which will not be obtained. Will the lack of mechanical rigidity take out a battery like the BLRFM12_55 before it is charged to death by the car (or succumbs to Southern California heat)? I don't know. Wish I did.

 

As I have stated in your other thread, where you focus myopically on this particular behavior in your car, I do not see this same behavior in either of my Prii. You cannot, therefore, extrapolate your observation across all Prii to conclude that they all excessively overcharge the battery and destroy them.

From my reading of the "several people [who] have discovered this over the years", it seems, mostly, that they do not drive their Prii enough for the car itself to maintain the battery properly, end of story.

 

The higher voltage in READY results when any current draw above the base for that power state is encountered. Turn on the running lights, it goes to 14.1 V, turn them off, it drops to 13.6V. Same thing with the fan, rear defroster, and so forth. The auxiliary battery isn't the cause of this voltage change, although a weakened auxiliary battery can result from it. Well, if the battery itself needs charging the current it draws while doing so will also trigger the transition to the higher voltage. I don't think the converter in the inverter cares what part of the car is drawing this current though, only that it does. I also don't know what fraction of Prius's do this. That it isn't reported more could be because very few drivers leave a voltmeter plugged in or the diagnostic screen on the MFD on while driving. Or some Prius may break this way. The repair manual is no help, as far as I can tell it is absolutely silent about what the "12V" voltage should be under these various conditions.

 

Like I said, I don't see this jumping to 14.x any time a small load is introduced. It goes up sure, depending on what is switched on. but it might go up 0.2 V from where it is at best.

The only time I see 14.x volts is if the battery is significantly low in SoH (70% or less), and I use this as an indication that I need to get the battery on the charger.