Can I use a battery tender?

Yes, it is safe to use it.
You have to be aware that you must disconnect it before turning on the vehicle.

 

How infrequent is your driving? If you're driving every 2nd or 3rd day, I wouldn't be concerned. OTOH, I think it's worthwhile for any driving behaviour, to hook up a low amperage intelligent charger perdiodically, every few months, let it run 'till it's happy with the battery's state.

A digital multi-meter for checking the voltage is also handy. It's not going to be as conclusive as a load test, but checking the voltage occasionally is good feedback.

 

The battery tender won't hurt.
Depending on how much down time your vehicle has, it might even help the Aux (12v) battery last a little longer.
I've wired the quick-disconnect plugs into my Motorcycles and ZTR.

I've used the $20 Walmart tenders for about 9 years now (I have 2) and they work as well as the $30 Battery-Tender name brand.

Unless your car is sitting idle for much of its life, I'd probably just replace the inadequate OEM battery with an Optima and not worry about it, but those are your options.

Good Luck!

 

I use my Battery Tender every winter on the Prius. Connect at the boost point under the hood. Much easier than accessing the battery. It's currently on the FJ Cruiser, my winter vehicle, because it's not winter.

 

A week or two, especially the latter, is pushing it. In cases like that I'll just hook up my charger before leaving. It's ok to be on indefinitely, CTEK 3300

 

Yes, I have one on my 2010, hardwired to the battery and stored in the plastic tub under the floor.

If my Prius will not be driven for more than a week, I plug in the BatteryMINDer brand battery charger/ desulfator/ maintainer, as it is safe for an AGM type battery as in my Prius. Some battery tenders are NOT safe for a sealed AGM battery. Check before you buy.

 

I use the extraordinarily cheap $5 (with coupon) battery maintainer. It delivers no nore than 12.8 volts, so it's really safe.

Automatic Battery Charger - 12V

I rigged it with a 3 amp fuse and a connector like that used on the Battery Tender brand.

Works fine.

 

No, windows can stay tight shut. The BatteryMINDer will not cause any battery gassing. Also, the Prius battery has an external vent tube through the floor.

 

While a load test is certainly the most accurate, since the battery doesn't "start" the ICE it may not be as useful for the Prius. This information from the manual seems to cover the situation. I use a cable connected to the battery with leads in the back seat. Then look at the meter through the window after the 20 minutes so as not to disturb the measurement with any other activity. Also note that the battery is always at some nominally small load running the computer and door lock communications.

12-volt battery Open voltage at 68 °F (20 °C):Manual page 567
12.6 - 12.8 V Fully charged
12.2 - 12.4 V Half charged
11. 5 - 11.9 V Discharged
(Voltage is checked 20 minutes after the hysystem and all lights are turned off.)

 

Owners Manual says 4.2 amp max, page 563 (in mine).

 

The 12V battery is "motorcycle sized". I use a 3 Amp "Battery Tender". Any of them that put out 2-4 Amps should be fine. You want one that is designed for over-winter use on motorcycles/quads. They won't overcharge the battery. Do keep in mind -ANY- unit will cause the battery to loose a bit of water. Whether that means it will shorten the life of the battery or not depends on how much water will be lost. Most of these won't cause a noticeable loss.

 

I highly recommend the battery maintainers that test for optimum voltage and apply a charge as needed.

I made my own "battery maintainer" once, which was a 12V power supply from an old electronic gadget. It tested at around 13V if I recall, and it was wired to a 12V plug, and plugged into the lighter socket which was "always on." I plugged it in in the fall, and when I returned in the spring, my battery was bone-dry. Trickle-chargers are not the answer.

 

I'd say look for the word "maintainer" and avoid the word "trickle."

 

One of my buddies used one on his motorcycle, and left it on for a couple of months while he was gone, and the motorcycle caught on fire, and burned a part of the garage. After that, I haven't used a battery tender on my motorcycle..

My 2 cents is NOT TO WORRY ABOUT IT.

I've been on 2 weeks vacations, and all of my vehicles would start up fine afterwards..

I guess if you are really worried about it, you can just purchase a battery charger and charge the battery when dead. But if your battery is dead within a week, then I would recommend getting new battery anyways, as it's probably not reliable.

I have a battery charger, for a quick charge for my motorcycle and other vehicles. Once in a while my kids would leave the all of the interior lights on in the minivan, or for whatever reason, the headlights didn't auto shut off (kids left one of the door open)

 

I've been using a battery maintainer on my Dodge Ram for over 2 years, and I couldn't be happier. The computers use a small amount of electricity, and the battery is sure to be depleted after a few weeks. Since I rarely drive it anymore, I keep it hooked up to a battery maintainer, which is wired to the battery and mounted in the engine compartment. The device has LED lights which are showing you when the voltage is being monitored, and when it's applying a small top-up charge.
This is the one I use: Schumacher 1.5 Amp Battery Maintainer/Charger - Walmart.com