I have 2 Lipo batteries and a Traxxas EZ-Peak Plus charger. Currently don't have a RC vehicle.

About 6 months ago I charged the batteries on the Store setting then did nothing with them till about 4 days ago. I wanted to make sure they were still ok so I went to charge both of them and it took several tries to charge without getting an error(the error was The charge cycle timed out without reaching the target battery voltage), are they still ok? I have no RC vehicle to test them on.

What capacity are the batteries, what rate were you charging them at, and what is the timeout setting on the charger?

Not familiar with that charger, but does it have an on screen digital voltage reading display? If so, what was the voltage reading of the cells at the beginning/end of the charge cycle?

Most LiPo chargers won't charge if any cell is below 3.0V due to the following risk:
BU-702: How to Store Batteries ? Battery University
Some chargers have a safety cut-off timer to prevent over charging cells... it's possible that one cell might not be peaking properly and if that's the case then chances are the pack may need to be replaced.

Without knowing individual cell voltages, it will be hard to diagnose.

Most chargers have several safety parameters built into them. On most hobby-grade chargers you can typically set maximum charging time, maximum capacity etc. The Traxxas chargers likely have these built into them and are not adjustable as they try to be less complicated so you may just be hitting one of these timers. You may be a tenth of a volt off and triggering the timer, sometimes if batteries sit for a bit they become a little "stale" and a few cycles gets them going again. It'd be best if you could take a look at the individual cell voltages which would give a good indication of where the pack is at. If voltages are within a tenth or 2 of each other it's likely the pack is fine, but if you see a cell that is far off of the others it's likely it has a bad cell.