I plug a Sears Battery tender into my cigarette lighter whenever I park my plane in my hangar. I have never had any battery issues. This inexpensive device can be purchased from any Sears store and can also be used to prevent battery drain while playing with your glass panels while the motor is not running.

Here is a link to the device:

http://www.sears.com/shc/s/p_10153_1...4&blockType=L4



Sears Exclusive. | Sears Item# 02871219000 | Model# 71219

Product Description

Charge your battery from inside the vehicle! Fully Automatic Battery Charger/Maintainer with Float Mode Monitoring for 6 and 12 volt batteries. 2 Amp, 12 Volt/4 Amp, 6 Volt slow charge with Reverse Hook-Up Protection is ideal for keeping stored, lead-acid batteries charged and power maintained at all times. Great for Motorcycle, Lawn Tractor, ATV, Snowmobile size batteries and to maintain larger Car, RV, Boat, Deep Cycle, Antique and Classic Car batteries too! Includes: 50 amp battery clamps, 12V accessory plug and permanent ring connectors for fast, easy charging every time. UL listed.