Chosen Solution
LiOn batts don’t use a straight line charger like other rechargeable batteries. In fact you could cause them to explode and/or catch on fire if you did! So the answer here is you need to use the correct charger & logic to charge your battery. You can’t externally recharge the battery as the battery is glued down so well you end up damaging it trying to remove it. You could put in a fresh battery in, thats your only option. As to altering your iPad to use an external battery - Not needed as you can do that now with one of these: LifeHacker.com - Five best external battery packs.
You may be able to get out of the boot loop with redsn0w.–perhaps put the iPad in DFU mode so it doesn’t attempt to light LCD? Your iPad should be able to power on via an AC charger alone. You can use a DC power supply to push charge into a battery–but very risky. I have done it before. I second the idea that this is a dock connector problem–I would start there. Jessa
