And cheaper to replace the battery when it dies.On the other hand the old traditional battery packs powered by a small 12V wet cell will have enough cranking amps to start an engine whether the battery is low, bad or missing.
Check the charge voltage as it is charging. Might be the charging circuit. Might be the battery. Might be a bad connection. Only a voltmeter knows for sureI have an Anker emergency jump pack that won't charge. I plug it in and the LED meter goes immediately to full. Leave it overnight, unplug it, and nothing. I think it's a Lithium Ion pack. Any ideas?