Warthogs are usually the best answer. I'll try and give some pointers.

1.) get rid of your vehicle depot and use it for a supply pad. 

2.) right away in the begining of the match you should be upgrading the warthog.

3.) make sure you have defensive turrets around because locust start coming in. 

4.) When your warthog is fully upgraded start spamming them out and sending them towards the scarab. Don't worry about losing some as they are easily replaceable.

5.) I know avoiding the power cells is an issue because they are easily destroyable, but look at the way the Scarab is pointing. On the SCARABS RIGHT side use that path and avoid going up the middle. You should not encounter any power cells using that path. 

Some final words of advice is to send the warthogs in groups of 5-6. It may seem like they're not doing much, but they do eat away at the scarabs health. 

Also use your mac blast it will help with the speed of taking down the scarab.

Good luck have fun =)

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