Best Way To Convert Abandoned Carts

I have a automotive parts store, sales are so so. In the past 5 weeks I have had 18,000.00 in abandoned carts. I already have my system send out a email 1 hour after they leave the site with a coupon code with $10 off their order. Any other idea's on how to get these to convert ?

I was thinking of upping it to $20 off their order? Eats into my margins but builds customer base ?

Retargeting.
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