Laying the battery flat on a CRT.5 will pretty much always result in it hanging off the chassis a bit if you're using some sort of battery holder. My custom chassis has about 3/4" more width to mount the battery than the stock chassis does, yet it still hangs over just a bit. I couldn't say if that's the case when using the RCM chassis and Tekno or RCM battery holder, as I don't own any of those

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SH Z-Car, Custom Crawler, 8s Savage,
12s XTM XLB 1/7 buggy,
4wd 4-link rear/IFS Pro4 truck,
Custom Hyper 10 Short Course,
Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz