maintaining charge in Gen 3 12 volt battery

I use one of these:

MULTI US 3300 - CTEK SWEDEN AB

It's an "intelligent", low amperage charger, with rudimentary status lights. You can leave it on indefinitely if you want, the last stage is trickle charging. I've yet to use it with our new Prius, though. A couple of thoughts:

1. The Owners Manual says to disconnect the battery (maybe remove completely from the car?) before charging. I think you'll be ok charging with it installed, but maybe someone more knowledable can comment. Do be careful to not reverse the charge leads. FWIW, I believe the CTEK will detect that and shut down.

2. With the Prius 12 volt battery under the floor of the trunk, my thoughts are to charge directly at the battery, and be sure to leave the hatch open, and floor covering off, to vent hydrogen.

Addendum:

Just to clarify, any time you charge a 12 volt it will give off some hydrogen. do not know how significant, but you want to keep the hood/hatch up when charging batteries. I've gotten into the habit of giving a good blow of air across the battery top just before connecting or unconnecting leads.

Any time you leave the hatch open, make sure to switch off hatch light. Not sure if dome light goes on: check that as well.

 

Use a battery tender, as you are in the US and they are a US company. You can order online if you like. It comes with a pigtail lead with ring terminals and a connector on the other end you plug into the cable from the battery tender. You can fasten the ring terminals to the boost terminal in the fuse box under the hood and the -ve one to a bolt on the firewall. The unit also comes with a pigtail with clips that plugs into the cable from the battery tender.

Do note that a Battery Tender isn't designed to recharge a dead battery. They only put out a few Amps, so it would take a few days to charge a dead battery (if it let you, as it may have some protection circuitry built in that may turn it off when it detected the dead short of a dead battery).

Mine is mounted on the wall of the garage. Been there since Pearl was young. Never had to use it. Hope I don't.

 

The Prius 12 vdc battery already has a vent tube that runs outside the car body to take care of that

I use a VDC Battery Minder, first on my Prius, and now on my FJ, as I can be away for weeks at a time on business

BatteryMINDer® Plus 12 Volt 1.33 Amp Charger-Maintainer-Conditioner (Desulfator) | All | Battery Chargers by BatteryMINDers.com

It not only maintains a "float" charge on your battery, it also desulphates the battery too. Have had great results

Here are photos of how I hooked up the leads on my 2004 Prius

In this photo I highlighted the battery vent tube





The Prius will not keep the 12 vdc battery properly charged in short trip use, especially if the battery is already partially discharged

 

Maybe.

Just my hunch: when charging, hydrogen production is much higher than normal. Couple that with the Owners Manual caution about disconnecting the battery when charging, I'd still be inclined to leave the hatch open.

The CTEK I mentioned does that desulphating phase too, fwiw. I asssume that's a good thing, but that's about the extent of my knowledge

 

Wouldn't it be better to get into the habit of not switching the charger on until the leads are connected and switching the charger off before disconnecting the leads.

 

The older model Battery Minders - which I have - put out 1 amp max. The newer models put out 1.3 amps max

Most regular battery chargers put out 6, 10, 15 or more amps while charging

The last thing I would worry about is hydrogen buildup.

With some of my seasonal equipment, I remove the battery and keep them inside. Leaving the Battery Minder hooked up all winter, I have never seen even a bubble.

 

Sealed lead batteries have internal catalyst that recombines hydrogen back into water. The only possibility of venting is when there is overcharge overwhelming the catalyst (charging current should be limited to 4A in Prius' battery). If that happens, battery will fail due to loss of water.

 

I actually do that. Connect up the leads, then plug in the charger.

I'm not sure but isn't there always a spark when you connect to the negative terminal. I'm really not sure: I know it happens when jump starting, but then the other end of the connection is hot.

 

There is -NO- gas leak in a sealed battery, except at the vent, which is routed outside. There can be a little hydrogen around any sealed battery, mainly because H2 molecules are so small they can move through most "solid" objects, such as balloon envelopes. But a battery case is pretty thick so I wouldn't expect much H2 to be present. Certainly not enough to combust, and absolutely not enough to combust explosively. At any rate, with batteries, it's the H2 and O2 -in- the battery that will explode bursting the case and spraying acid and plastic bits about in a hazardous manner. I see no flame path into the battery with the Prius unit or any sealed battery. So this is not a concern.

But taking measures to ensure you are safe is not a waste of time no matter how much it seems. So go ahead.

 

Hi All,

I was concerned about the 12 V battery running down on my 2010 Prius, until I read that the Gen III smart key system turns itself off after some period of time (a week?). This is unlike the 2nd Gen Prius.

 

Thanks for the info.

If any and all off-gas is routed to that vent tube, then I'm thinking to hook up under the hood, at that fuse box jumper location.

 

The CTEK power cord's maybe 6', and it's leads another 3'~4'. I can hook up to under the hood battery (or the Prius's under hood connection point), and have the charger flat on the ground beside the car.

As far as reach, a decent extension cord will solve your problem. There is a caution in the CTEK manual to not use an extension unless absolutely necessary:

An extension cord should not be used unless absolutely necessary. Use of extension cord must be used, make sure that:
a) Pins on plug of extension cord are the same number, size and shape as those of plug on charger
b) Extension cord is properly wired and in good electrical condition
c) Wire size is large enough for ac ampere rating 3.3 amp

Hmm: the charger is two prong. I don't think you would have issues though, plugging into a 3-prong ground extension cord.

 

Yes, I read that this is a good protocol to follow.