In 2007, I installed a sealed, lead acid battery recommended by a fellow aviator who sold caravans (permit aircraft). As far as I know it is still in the aircraft having spent 16 winters in cold, damp hangars with long breaks. One morning I discovered that someone had left something switched on and the battery was dead flat. Hand swinging started the engine and the battery does not seem to have suffered. The key is to turn the prop several times after switching on the fuel pump, as Jan recommends above. It always made me laugh when, on a frosty morning with several other mad aviators struggling to get their motors going, ours always started instantly. I could never understand why everybody didn't do it.