Three month stay

It's in the owners manual. As I recall it was 6 months min. It's -completely- disconnected, both sides, so only "self discharge" occurs.

Make sure the charger you use is designed for this. Most will overcharge the battery. A "battery tender" won't. They are designed for motorcycle and other rec. vehicle batteries that you leave for 6 months at a time.

 

To reiterate to the OP

Make sure you are using a correct battery tender that is fully automatic, to keep a "float" charge on the battery. The better tenders also condition the battery, like this one:

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

Never, ever hook up a regular full time "trickle" charger. If left on for a week, certainly for months on end, they will destroy a battery

I wouldn't worry about the NiMH traction battery. If it's in the low blue's on the display, there is a procedure known as "forced charge" that you can search here on the forum

 

I have left my 2008 for over 3 months without a tender twice.
Started right up both times when i returned home...
No problem!!!!

 

If you're worried about it, get the battery charged up before you head out.

Forced charging is accomplished by shifting to D, holding the brake pedal firmly, and stomping the throttle. The ICE should kick in and charge. Don't let off the brake, lest the predictable result will occur.

 

We left town for 2 months and the battery was dead. it was easy to jump start the battery. it has worked fine since.

 

Run a battery flat dead once, its life and capacity are diminished. Do it often enough, the battery is toast