2002 Kia Sedona Starting isue

Over the past week I have had an issue with my 2002 Kia Sedona starting. At first it acted like the battery was low, so I went to a place and they checked the battery and said it was fine. Drove it for a week and no problems it started just fine. Then it started to act up again, so put a battery charger on it for 5 hours, and then went back and had the battery checked and the alternator and both registered fine. The left that place and went shopping, came out about 30 minutes later and it would not start. NO crank no nothing, you turn the key, all the dash board lights go on but nothing. No sound, no clicking now try to start, dead nothing. So had van towed to mechanic wh was closing and will look at van on monday. I went over today to get something out of the van and thought I would give it one other try and it started right up, like there was no problems. So I shut it off, waited a minute or two and tried again and it started right up without any problems. So what might be causing this issue? Also, last week when we stoped the first time to check the battery when we opened the hood we got a whiff of what smelled like burning wires, but didn’t see anything and that was the only time we smelled that as I checked the engine each day after that. Could some wire that is a ground have gotten burnt?

If this is not a maintenance free battery, checked the cables and make sure they are connected well and no corrosion. The battery isnt putting out juice you just have to figure out why. It could possible be a short. There is a small chance is could be at the alternator but those typically give warning