A new shipped battery should have a 40% charge ideally. In this case the battery had none, boot loops most often occur because of battery issues and incorrect shut down. As the charge is applied Ipad starts to boot, this creates boot current draw that the usb charging circuit cannot provide (normally this comes from the battery!) Triggering temp sensors can allow a boot charge to gather giving the battery enough energy to meet the boot current demand, then be shut down properly then of course charged in the normal way.
However if this happens with a new battery I would strongly suspect the battery, you should never seal a case after changing a battery, until the Ipad has been booted and all functions checked!
I have observed a number of cases where a battery low signal has been shown when plugged in, applying moderate heat to the rear casing has within a minute allowed the ipad to boot and show a good charge level, in all these cases a malfunctioning Li battery pack was identified as the cause and changing them resolved the issue. (these cases typically presented as "I put it on charge last night and it was stone dead this morning!".
If plugging in your charge cable triggers any life then it is not your charger, port or charging circuit almost certainly battery. If you have a boot loop apple logo restarts and you do not have jailbreaks installed it is almost certainly battery charge condition < the real question here is why on earth these devices are not setup to shut down automatically at 4% or so charge level to prevent such a scenario!! Maybe Appleinc could chime in and explain it to me, especially when a device absolutely must have minimal input froma battery to boot or it will enter an almost inescapable fault state to the end user!!!
Hopefully some may find my comments useful
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