What kind of load are you powering using the SBV? Without expansion batteries a runtime of about an hour at full load is normal. When you're charging it, are you doing so using DC or AC? Do you have any minimum or maximum charge level limits set, or a charging speed limit? If so, remove those and fully charge (until it stops taking any power), then discharge (until it powers off on its own), and charge it again to recalibrate the battery.