This model of DVD Player is made primarily for Walmart Stores so am Assuming you bought it there. Battery Swelling is an acid combustion issue, meaning they over-expired or over charged. Don't leave these charged for too long. Other than recommending to get the replacement that is mentioned in the original Users Manual that came with it, it's quite difficult to get a replacement. I have added a site below for walmart purchases that may be compatible with your unit.
Unfortunately, without getting an exact genuine replacement, there is a down side to the Universal Battery. They claim to hold up to 11 hrs, but the average usage is about 5 hrs constant use. So you figure instead of 4 full length movies maybe 5, you might get about 2-3 movies if you're lucky. Trial and error and user results vary obviously.
And you may wish to check with Walmart. I believe this unit had a recall on it due to faulty wiring and or battery issues that cause a fire hazard. Silver Durabrand DVD Players as well as Purple and Pink ones were recalled. I would take it back if that is where you bought it and ask them about the recall. Or check with www.cpsc.gov
to see any updated info.
Wish you luck.