Aluminium Peterbilt Battery Box Toolbox Bottom Replacement Step for 379 388. Aluminium Peterbilt Battery Box Toolbox Bottom Replacement Step for 379 388 389. Quality Part with Aluminium, Durable and reliable during various weather conditions. 29.5″ Length, 7″Width, with a mounting arm 14.4 Length. Any product you return must be in the same condition you received it and in the original packaging. Please keep the receipt. We usually respond within 24 hours on weekdays. Thank you for shopping at our store.