12V Battery Keeping Charged when stored

Most common method I know is a trickle charger. It provides a small but constant charge. There are even solar trickle chargers. I've seen people use the solar trickle chargers when they were leaving their car in one spot for a few months so it would be ready when they got back -- fluids, seals and gaskets are a different problem but you shouldn't be gone long enough to worry about them.

 

A few alternatives come to mind:

1. Use a battery tender
2. Charge the battery fully with a regular charger, then disconnect it per #3 below.
3. Disconnect the negative battery terminal, or disconnect the positive lead under the red jump terminal cover at the main relay/fuse box near the inverter

 

Another suggestion -- shut off the smart key system before storing the car. The switch is under the dash to the right of the driver.

 

I think the Patco charger is a good one and doesn't drain your battery if left disconected from the AC when the battery hookup cables are connected, alot of other chargers will.
Some negatives are you have to connect the battery hookup cables prior to plugging it into AC and it's a little heavy.

http://dkc3.digikey.com/PDF/T081/2219.pdf
Patco 150 1.5 amp 12 volt Digikey part# PATC-03-ND and Battery hookup spring clamp PATC-07-ND or you could save some money and make a hookup cable with a soldering iron, Battery hookup spring clamps and wire.

 

A trickle charger can destroy a battery if left connected 24x7. They will supply current whether the battery needs it or not

There are battery tenders that are "smart" and can be left connected 24x7. I use this model

 12 Volt-1 Amp  Charger and Maintainer

 

While this is prudent, it will not reduce the parasitic draw on the battery significantly. The SKS system draws very little in the grand scheme of things.

 

I'm not using one but here is a link tojust one of the solar chargers I found:
Northern Industrial Solar-Powered Battery Maintainer — 1.8 Watt | Solar Solutions | Northern Tool + Equipment

 

Be aware unless you modify your Prius, you won't have any luck charging with a solar panel through the cig. lighter or accessory power plug when the car is off. You will have to do your own wiring to accomplish that.

Your battery should not loose much charge in a few weeks. If you are storing the car for two months or more, then yes, you should do something to keep the 12V battery charged. Either disconnect the -ve lead or get a battery tender. The tender can be connected at the front underhood boost point, BTW.

I purchased the Battery Tender Plus listed here:
Batterytender.com - Home of All Your Charging Needs 2008 Catalog

If your battery is loosing charge in just a few weeks, then the battery is bad. It may have been damaged by allowing it to fully discharge during shipping to the US, or when it sat at the dealership.