12 Volt Battery Service

I am wondering how often Prius drivers service their 12 volt battery? The 12 volt Prius battery being located under the trunk floor is kind of “out of sight - out of mind”.

Although the Prius AGM battery case stays fairly clean and the terminals do not get heavily corroded, the terminals still get a layer of oxidation. It is the gray/black colored film that covers the terminals. This film creates resistance, voltage drop and shortens battery life. A clean terminal is bright and shiny.

Servicing the battery generally involves:
· remove the battery cables and hold-down bracket(s),
· clean the top of the battery case, terminals and cable ends with a battery cleaner,
· using a battery brush with soft brass bristles, lightly brush the battery terminals and contact areas inside the cable ends until they are bright and shiny,
· reinstall the battery cables and hold-down bracket(s),
· coat the reinstalled battery terminals and cable ends with a battery terminal protector.

This is an inexpensive and easy task that if done once per year will prolong battery life and keep it in top condition. I just cleaned my battery which is now three years and 50,500 miles old. The resting voltage is 12.8 volts and the car has had no battery/electrical problems. Below are the three battery cleaning products I use.

Not mine. The terminals and clamps were clean to start with, and since they were tightened enough to form a gas-tight seal, opening them up to clean them would only create the possibility of trouble.

It is not possible to create a "gas-tight seal" by just tightening the battery cable clamps. The metal surfaces don't fit together prceisely and the clamps don't stay tight. Also, electricity flows along the outside of a conductor, not through it. That is why corrosion occurs on the outside of the terminals and clamps. All theses conductive areas, not just where the clamp contacts the terminal need to be sealed to prevent corrossion and resistance, which the purpose of coating the reconnected cable ends and terminals with a battery terminal protector.

If you really think that "opening them up to clean them would only create the possibility of trouble", perhaps you should just leave things alone, but that is just a rationalization for doing nothing, not a thoughtful approach.

Your Prius 12v Battery is SEALED (with an over pressure vent tube) so battery acid will not cause the corrosion common in lead acid batteries. There is no need to ever clean the battery. Checking the connections to make sure that they are tight, measuring the battery voltage with your Prius off (It should be more than 12v) and again with the headlights on (the voltage should not drop below 12v) once in a while are the only maintenance items that may be required.

JeffD

As I implied in my original post, it is true that the battery is vented outside the battery compartment and doesn't have a problem with battery gases causing corrossion like other batteries that are not outside vented. However, oxidation, which is what is addressed in my original post, also occurs from the surrounding air and moisture. This gray/black oxidation looks normal to the unaware, but it is actually causing voltage loss, reducing battery power and shortening battery life. It pays to keep your battery healthy, if you want to insure high performance and reliability of your car and extend the life of your battery. The Prius battery is low maintenance, but not maintenance free.

My OE 12v battery was still good after 8 years and 215k miles with NO maintenance (due to long trips and never discharging the 12v battery) when I replaced it with an Optima Yellow-Top.

JeffD

What about the traction battery which is in the same compartment and must be subject to the same corrosion?

Actually, you very likely get enough plastic deformation of the metals to create a small gas tight seal, or seals. A circular seal area even 1 mm in diameter would probably work well since there is very good heat sinking around the contact point.

Also, the "skin effect" for current being distributed to the surface of a conductor applies only to AC circuits.

There's another recent post mentioning checking the water levels:

12 Battery Maintenance | PriusChat

Also: it's worthwhile hooking up a low amperage trickle charger, just a token level of charge is needed, before disconnecting the battery, to maintain memory.

(I tried PriusChat's search function and completely struck out. But just using Google search with a few key words I remembered: it was the first search result)

Addendum: Just had a look at ours. It says "never add water", and has opaque black case. I believe it's not like traditional lead-acid battery, has liquid, but not sloshing around: it's in some mesh medium. Guess I'd just leave it alone.

the secret to longevity of the prius battery is buying the prius before it sits around on the dealer lot and never letting it discharge. my 04 lasted 8 years, my 08 is coming up on 5 years and i expect my pip to do as well. if you bought your prius after used, or after the dealer had it more than a month or two, or you let it discharge by leaving somrthing on, all bets are off and i don't know if cleaning the terminals will extend longevity or not.

The early (Gen1 2001=2003) Prii HV batteries did suffer from corrosion of the "Bus Bars", but that was due to leaking electrolyte from the HV Battery Modules, not the 12v battery. Corrosion has not been a problem since the HV battery modules were improved for the 2004 model year. The HV battery modules were improved (reduced effective series resistance) again for the 2010 model year Prius.

JeffD

Or get one so long on the lot that the 12 volt is totally dead, and get it replaced prior to the sale. That was our situation.

Well, my '06 12v battery after 6 years of silence was dry as a bone, filled it with distilled water, charged it and it's holding a charge, put it on the lawn mower, so I'd clean the teminales, coat the connections with a dielectric grease, fill the six chambers with distilled water, once a year and top off with a 2amp charge once a month for longevity,ymho,ymmv.

HAH ????

This is only through for quite high frequency AC and we are not talking about the 60Hz neighbourhoud !!

So the AWG rating just bogus right NO need for thicker cable for higher current !!!!

Where did you get this ??? I am E.E so please believe me AC and even home DC is flowing "troughout" the cable material and thickness does mattter (other example fuses !!)

I put a drop or two of "bar & chain oil" on each battery post when my Prius was new (3 years). Bar & chain oil has a sticky additive making it cling to metal and gives a long lasting air / moisture tight seal.

I do this with all my batteries, AGM and flooded cell. It keeps the terminals free of corrosion.

You are technically correct. I should have said electricity flows along the outside of a conductor, and (instead of not) through it. In either case, it remains true that corrosion and oxidation occur on the outside of the wire and between the connector and terminal which is a cause of voltage drop, which is the real issue in this discussion. Voltage drop is actual voltage that is lost so that the voltage is lower at the device than at the battery. It is important to keep voltage drop to a minimum because devices work less efficiently, or not at all, at voltages lower than the voltage for which they were designed; and, it shortens the lives of the battery and devices.

At the extremes there is always a debate between the "perfectionists" who do more preventive maintenance than needed without regard to cost; and, the "lemon-makers" that spend little or nothing on preventive maintenance before they unload it on the next owner/victim, the "lemon-eater". I am neither a perfectionist nor a lemon-maker. Cleaning your battery is not extreme. It is highly cost effective, normal, preventative maintenance. Do it and you will get on average an extra couple years life out of your battery, protect sensitive electronic components, maintain your car's performance and reliability and spend less time and money in the repair shop.

You are NOT correct it will NOT flow outside ever ! Energy maybe in some very "interesting" cases again you are wrong. In an automotive setup NO electricity will "flow outside of a conductor"
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It seems to me you do NOT really have even the basic understanding about this. Yes voltage is dropping but it is because of the resistance (increase) at the contacts (which are not perfect any more due to some corrosion) this is not what damage anything ... most stuff in your car has its own DC/DC converter built in and will be happy with the "dropped voltages" probably way down when the batter is already dead. Please if you do not understand this just leave the details out....or to the "perfectionists". And if the car is able to start (well before devices you mention even come to life) the HV WILL maintain the desired "voltage".

The only valid point is that THE car becomes less efficient ... and maybe you can not fully charge the battery. However you are 100% right that it is a good idea to keep the voltage drop due to some corrosion on the terminals to the minimum and that can be done with some LTC ... but the rest of semi scientific thing PLEASE !!!

This part is OK with me personal opinion something which is not measurable

I said "along the outside" not outside. You are distorting what I said.

No I am not !!! This still totally incorrect .. leaving out the details current WILL NOT flow outside of the material. ENERGY in form of "electromagnetic field" effect introduced by the conductive material and current may. There is NO current in vacum but of course ENERGY can flow through ... I know this is black magic.g

So chill I am not distorting anything .. NOTHING goes OUTSIDE of the conductive material (in any of the Prius use case anyway ... ) ... however surface oxidation/corrosion is a possible issue but not for the reason you stated ... that is all.

Current can and does flow through a vacuum if it did not the old style radio and tv valves "tubes" would not work.
It has also been proved that high voltages travel along the outside "skin" of a conductor.