Leaving for 2 weeks and need a Battery Tender

the one on priuschat is not a battery tender for a 12 volt battery, it's a hybrid battery conditioner. how old is your 12 volt battery? you'd be better off with a healthy one, then you wouldn't need a tender.

 

You don't need a tender. If parked in your garage, just make sure you don't lock the doors.

 

You have other options...there is a button under the steering wheel to turn off the SKS (smart key) system which is part of the reason why Gen2's show some 12v battery discharge on trips. That's all I do to be honest. Harder but you could disconnect the 12v battery, maybe it's easy to reach the negative lead behind that little plastic panel in the back beside the liftgate, where you change the rear light bulbs.

When you get home, warm the car up in Park for a few minutes to recharge up things. For some reason our HV battery goes into purple quickly after the the car sits a few weeks. We just had that happen, but the warm up helped recharge before we drove off.

 

This is a good smart charger. I've used older versions before. I see this one claims AGM charging which is what you need.

Two weeks isn't that long, but we don't know the condition of your battery. Maintenance charging never hurt.

I presume you know where the battery is on your car. You'll have to pull the trunk tub out.

For longer periods it would be best to have someone start it periodically.

 

Not driving your car for 2 weeks should NEVER be a problem. Just proceed on your day and pretend nothing has changed. Don't worry about something that's not worth worrying about.

 

Two weeks is borderline. Might be a problem upon return. Invest in a low amperage smart charger, something that can be left on indefinitely. Cheap insurance, and down the road it'll likely be needed again.

I use a CTEK 3300. Not saying it's the best or only option, just an example, one that was readily available here.

 

To the OP, I would do what wjtracy suggests. Now if you are interested in a GOOD battery tender/charger take a look at the "Battery Minder" 12248. You can find it easily with a Google search. That is what I have. It has rejuvenated a few batteries that were sulfated and made them work again in traditional ICE vehicles. It also works well with our Prius. Used it on both the old Gen II and on our new Gen III. Simply attach to jump post under hood and don't worry about it.

The Battery Minder also comes with terminal ends that can be attached permanently to the 12 volt battery. Once that is done, you simply connect the battery minder and plug it in as needed.

I would not recommend the tender you pictured. I don't think the algorithm is correct for the AGM battery that is in your Prius. Whatever you do, remember if you charge and or maintain your 12 volt battery, ALWAYS use the AGM setting. Some will say not to exceed four (4) amps when charging. Just be careful, and don't take shortcuts. Some times spending less can cause more damage than spending a little more. Is the battery minder pricy? Yes, if too expensive look at the various CTEK models that are available. Bottom line, don't cheap out. Buy a good high quality product and you should have it the rest of your lifetime. Finally be aware of the polarity of your devices and the Prius. Under NO circumstances should you ever reverse the polarity. When doing so you risk thousands of dollars of damage to your beloved Prius.

EDIT: After reviewing the info posted on the spec sheet, I must say that they do advertise this unit as sufficient for AGM type usage. The max output is kind of low though, so if you needed a charger rather than a maintainer, the unit you are interested in would NOT fit the bill.

Just my two cents worth.

Ron

Best of luck to you,
Ron (dorunron)

 

I would vote for this except.......if the battery is the original OEM, it's approaching 8 years old and might not survive two weeks without use.

ANY name brand "smart" battery maintainer/charger will work just fine.
WalMart has Schumacher, I think. The Battery Tender brand is good too.
Any auto parts store should have a couple to pick from.
Any that costs over $40 is more than you need.

 

I would still make sure that the charger/maintainer that is being purchased has the AGM setting.

I have seen NEW "smart chargers" out there or at least labeled that way that did NOT have a AGM setting. Look closely on the shelves at WalMart. I bet you will too. Name brand also...

Ron

 

1. The good news is that your daily driving pattern is such that the 12V battery should be fully-charged.
2. Unfortunately since you don't know how old the battery is, it might be marginal and may not last for 2-1/2 weeks. 18 days x 24 hours/day x 0.02A quiescent current draw = 9 Ah. A new battery, fully-charged has capacity of ~40 Ah, so clearly you would have no issue with a new battery that was fully-charged. A marginal battery, fully-charged may have capacity of half that amount or less, who knows.
3. Hence, if it is important that the car function upon your return, I suggest that you either replace the 12V battery now with a new battery that was fully-charged prior to installation, or hook up a suitable battery charger to keep the battery topped off while you are away.
4. If you decide to buy a charger, I would suggest that you invest in a decent battery charger with an AGM position. The current output should be 10A with a switch to reduce output to 4A. The one you identified is not suitable simply because its output is limited to 1.5A maximum. That unit assumes that the battery is always going to be fully-charged and that all you need is to maintain that charge. That set of assumptions is not always going to be valid.
5. I don't see the point of leaving the doors unlocked - actually one benefit to locking the doors is that if the car refuses to lock, you know it has a problem - for example a door is ajar. Leaving a door open would be very bad from the point of view of draining the 12V battery.

 

Be advised, you are looking at the MFD display which shows the state of charge for the hybrid battery. There isn't a state of charge indicator for the 12V auxiliary battery. Well, you can make the MFD indicate the 12V battery voltage. Follow these steps or get yourself a digital volt/ohm meter (DVOM) and measure the voltage at the battery terminals or at the jump terminals under the hood.

 

Agreed 100% The battery read out on the Gen II Prius (Blue, Green, Red) is only for the traction battery. I did miss that tidbit when reading the OP's post.

You can check it with the MFD if you do the test that is linked above and in my signature file. However your best bet is to measure the 12 volt battery voltage level itself with a GOOD digital volt meter AFTER the battery has set OVERNIGHT.

Refer to the chart below for more information on specific voltage levels as per State of Charge. IF your voltage is below 12.3 volts after sitting ovcrnight, I would then replace it with a "FULLY" charged battery as Patrick Wong suggested above. Also note just because a battery is NEW does NOT mean it is fully charged. Again refer to the voltage level of the specific battery and the chart below for more information.

Peace,
Ron (dorunron)

 

I have a battery tender which works fine an agm or regular batteries. its not a charger, but if you leave it on long enough it will charge it up. use it on my bike and chevelle which sits for months sometimes.

I'd take a look at the battery; it may have a date code, or be marked when it was changed if it was. if it appears to be 8 years old, replace it.

 

If the installed battery is GS Yuasa (which is the original equipment supplier), the date code will be on top of the battery, hidden by the battery bracket. It is in DDMMYY format.

 

Recent smart chargers do not have a specific setting for AGM because they are "smart" enough to adjust automatically.

Not true at all. Unless the battery is SO dead that it is beyond help, even a 1.5 amp charger will give it a good charge again if left connected long enough......like 24 hours for instance.

And once again, it is not necessary to have a switch labeled AGM because it is quite simple to make a charger that works well with BOTH wet-cell and AGM types with no operator intervention at all.

The important part is that the operation of the charge is truly automatic.
Trickle chargers won't do and your 10/4 amp unit might not either if it doesn't automatically switch to float or off when the charge is full.

 

Regarding battery install dates, I'm resolving (next time I'm replacing one) to just mark it myself. Kind of like what we do with a new hot water tank.

 

Like minds think alike. We mark ours too. Just had the heater changed. Date plainly marked with Black Sharpie...