Can I use a battery tender?

The only downside to that plan is that each time it goes dead, it damages the battery. Sometimes it won't even take a charge, and you'll need a new one. If you can find a deep-cycle battery, or an AGM, it will stand up to such abuse a bit better.

 

I have one of these on my subaru which i just use in the winter. So i keep the battery topped off with this solar charger, and i installed slotted rotors to help clear the rust off the brakes.
BatteryMINDer 12 Volt Solar Charging System with 5 Watt Panel and Desulfator, Model# SCC005 | Battery Maintainers| Northern Tool + Equipment

If you have a dedicated parking space next to some grass, you can mount it on a pole next to your car, it has a 20ft quick disconnect cord and a 4 foot cord for your cars side, which you can just run out of the hatch.

For my subaru, i attached magnets to the back of the solar panel and keep it on the truck lid. Then i deattach it and put it in the trunk when i use the car.

Your method of jumpstarting a car will work up to a point. But when you leave a lead sulfuric acid battery sitting dead for too long. Due to the lack of polarity, the metal plates begin to build up a layer of sulphate, which makes them more and more useless to taking a charge over time. Keeping the battery topped off, but not overcharged is the best way to store a lead acid battery.

The other alternative is if your car is in a garage, or next to your house. You can install a normal battery tender. These also have quick disconnects, i used them on our motorcycles which were garage kept for many years and never had a problem. I used Yuasa units, which are of good quality and sold at most motorcycle shops.

 

"Your Buddy" probably used a trickle charger, or didn't buy a very good battery tender. He most likely left it on "trickle" of 2Amps, which ultimately would overcharge the battery and catch it on fire if left like that for several days.

I used a yuasa battery charge/maintainer on my motorcycles, and when the battery was fully charged, it would switch to float charge and sit like that in the garage all winter. The yuasa has a nice visible led indicator to show it's in float mode which is nice. Here's the one i used on my bikes, and would certainly work on the prius:

 

This is the best plan I've seen yet. A battery tender/maintainer is the only way to protect a battery over long periods of inactivity. The disadvantage to using a cord is that it's not always available and can become unplugged while you're away. The solar panel solves the problem.

 

I agree, using a trickle-charger beyond a day or two is a bad idea.

 

12.8V is safe indeed but will not charge lead acid battery much or at all. The minimum charging voltage is 12.9V. The float charging (what the OP wants) is done at 13.4-13.8V (depending on battery type: gel, fiber mat, or flooded).

Watch the HF chargers closely. They are know to fail at high voltage settings.

 

To the OP. Whatever charger you buy, make sure the current doesn't go over 4A (initial charging) and the voltage doesn't go over 13.8V (when fully charged). The specs printed on the charger can mislead. I recently bought a cheap lead battery stabilized charger (for this very same application) that supposed to output max 1000mA/13.8V, but it did at 14.15V, that's too much for float charging. Had to return it.

 

Our classic Buick Skylark dos not get driven in the winter, and will go weeks in the summer without being driven. So I have always kept the battery hooked up to one of these inexpensive "float chargers":
Automatic Battery Float Charger
By keeping the battery on a float charge, the last battery in the Buick lasted 7 years, and it was still working fine, but I no longer trusted it as it was so old, and did not want risking getting stranded somewhere. The "float" actually works to lengthen a less used batteries life!

For the Prius, I am considering buying one of these "Battery Brain's" that auto disconnect the battery if it falls below a set voltage. All you have to do is push the button on the battery brain, and it re-connects the battery to the car circuit, and allows enough reserved battery juice to still start the car.
(Sorry, the link for the Amazon Battery Brain will not stay in the post for some reason. Do a search at Amazon for "
Battery Protector (T1) - 12V")

The only reason i am considering the "Battery Brain" for the Prius, is we take 2 to 3 week vacations, often, where the Prius would just sit, possibly at the airport, for that long. If you are just leaving your Prius sitting for less than a week, I would not worry about it.

 

Is this the one?

 

I had a bad experience with a similar "battery-maintainer." Although it tested at a "safe voltage" it still destroyed the battery, because it never shut off. A proper battery-maintainer must test the battery voltage periodically, and apply a trickle charge until the battery is topped-up at full charge, then stop charging.

 

This is not correct. Look up float charging. Telcoms do it and get 10-20 years from their batteries on float charging. It has to be done right, though.

 

All battery maintainers use voltage regulators. Whether its done with relays or semiconductors depends on the era in which they were made. The caution still remains; make sure it's a proper battery-maintainer, not a glorified trickle-charger.

 

I've used a Battery Tender both outside in the driveway (it's rated for outside) and inside a garage. My Harley with the alarm will drain the battery for sure if it sits for over a month. (it is supposed to go into a lower drain state after a couple of weeks, but it still drains it).
In 10 years of using these products I've never had an issue. The batteries last for years this way. It also can tell me there's an issue a head of time. The only thing I've done is made sure they work with AGM batteries. The original one i had was not made for them.
My dad saw what i was doing, and wanted one for his car. He can leave it parked for 3-6 months at a time when he's doing his snowbird routine. Car starts right up and the battery still lasts him several years without issue.