Lithium batteries are getting cheaper all the time.
My car's battery is on the way out so I've bitten the bullet and bought a LiFePo4 battery. These are the latest technology for bikes and cars and are much safer. Lithium Phosphate are the replacement for the old Li-ion.
I can't stand the monster lead acid battery in my car that wouldn't be out of place in a Greyhound bus. It weighs in at about 25kg. It's a biggen because my cars diesel so it needs plenty of cranking power and it's rated at 780CCA.
This little LiFePo4 weighs in at 2.3kg and pumps out 800CCA! and is a 45 amp hour. A replacement lead acid is about $250 (not OEM) and this is $540 delivered so I was prepared to go the extra $300 to save the planet. These new batteries last about 5 times longer and are environmentally friendly as they pose no threat once they're done with.
The battery is generic and comes with terminal blocks with M6 threaded holes. It can be mounted standing up, on it's sides or ends or upside down.