Review on Bussmann RB-BI-70A: High-Performance 70 Amp Battery Isolator for Optimal Electrical Efficiency by Lucas Hale

I use this to disconnect my battery and ham radio from the Astron RS-35A power supply. Just connect a good DVM and a few amps load after the isolator and adjust the PSU output with an internal adjustment in the PSU so you see 13.8V. If you connect it to your batteries and devices under light load, you should see 13.8B. If you don't tighten the PSU like it should. Much easier if your power supply has external voltage regulation. That way, the power supply won't slowly drain your batteries if the power goes out. If the crowbar's circuit fails for any reason, you won't have accurate shots with your batteries.