I'm on oxygen at night and wanted a backup if the power failed, so I bought these. They are big and take up a lot of storage room, but that would be worth it if they would run longer. I plugged in a small (14"x12") blowing heater to see how much I would get out of one battery. ONLY 2 HOURS! It was fully charged. $4000.00 later.... I'm disappointed, to say the least.