The FePo4 batteries are the newest car technology out now. They only weigh 10lbs or so depending on the sizes, but so far most won't work with a typical alternator.
They are current limited to below what most alternators make, but some seem to be coming out that are car sized and say they are usable in place of one battery. Those look to run $500-$700 so far, and none list sizes by proper car type(type 65 for example). Hopefully soon those will become common in needed type sizes, that we can afford for most cars.
92 Mark VII LSC SE - soon OBDII and 4R70, GTC kit and 347, custom paint.
98 Explorer Limited project to add 4WD, XP8 parts, KB blower, paint, 337.
99 Limited mail vehicle, SOHC 4WD, later 306/4R70W swap. 1998 Mountaineer spare. 72 Ranchero 351 Clevor project.