After you remove them perform a vacuum test. The one under the battery is for the tilt and has a check valve in it. Attach a vacuum pump/connect to a running engine to the fitting that goes to the intake manifold. Attach a vacuum gauge to the other fitting. Apply vacuum and then stop, the number doesn’t matter, it should not leak down. If it does then you have to decide whether to clean off all the undercoating and try and find rust holes. If the check valve is leaking its shot.
The other tank under the hinge is for A/C and does not have a valve in it. For this one you need to plug the small fitting and attach a hand vacuum pump with gauge to the other fitting. Apply some vacuum and then stop and watch for the gauge to drop. If it does then you have holes.
Since both are reproduced and don’t have to be cleaned up that could be the way to go.