Re: Does my nexus 7 have to have factory charger and plug to charge
First off, chargers are universal. They all put out 5V by default. Some are higher amperage than others, but all are capable of charging any USB device. Even your computer can charge your device. BUT, it is worth trying your charger and cable on another device to make sure it is actually working.
Not to go all Princess Bride here, but a lot of batteries that seem to be dead are only MOSTLY dead. Allow me to explain. No, is too much. Allow me to summarize.
A Lithium battery cannot be recharged if it is allowed to fall below a certain voltage. In order to protect it from doing so, a controller cuts the battery off at a voltage much higher than that (the "cutoff voltage"). Your device is actually programmed to shut down gracefully and refuse to start at a much higher voltage so the battery controller doesn't have to do its job. Once the controller has done its job and cut the battery off, the controller will not allow ANY battery usage until the battery voltage rises well above the cutoff voltage. And the controller will only "allow" charge to flow in slowly at that point, because at the extreme highs and extreme lows of charge, the battery is in its least stable chemical state. Thermite. You don't want it.
So if your battery controller has kicked in and shut the battery down, it's going to take a while to put enough energy into the battery for the controller to be "comfortable" flipping back to quicker charge and allowing your device to start up again.
Best advice I have is to test your charger to make sure it works, plug it in to your device, and leave it alone for at least a few hours. Overnight is better. If the controller can recharge the battery, it will. There's nothing you can do to help other than just let it do its job and leave it alone.
If after 12 hours or so there are no signs of life from the battery, then it's really dead and the only thing you can do is go through its pockets for loose change.
The Nexus 7 2012's battery is rated "moderate" for replacement by ifixit. They sell tools that make it easier.
A replacement battery can be had off Amazon.com or other reputable sellers for $20-40 (slightly higher if you want a larger capacity battery than stock), or eBay has them as low as $15. Just make sure you get a "first generation" battery because I think they changed the battery in the 2013 model.
https://www.ifixit.com/Guide/Nexus+7+Battery+Replacement/9895