It's not clear to me what he is trying to accomplish. If the battery switch is set to "both", both batteries will be discharged equally, regardless of where the pump is physically connected. If the switch is set to "1", "2", or "Off", and the pump is connected directly to one battery, only that battery will be discharged. The other battery will be unaffected. On 2018-04-26 11:58 AM, Rich Gano via Trawlers-and-Trawlering wrote: > So a friend has a 25 foot sailbote which has two batteries independently > connected to a 1/2/BOTH/Off type battery switch and he has to leave it in > the water with no shore power available for an extended time. He wants to > leave his one bilge pump connected directly to one or both batteries > (probably with the battery switch in Both) but is concerned about the chance > of a failing battery dragging the other one down with it. > > So a question for the electronics gurus. Can he find a switching device > which will sit between the batteries and his pump which can shut down a > power leg to a low voltage battery? I guess a Blueseas ACR could function > here, but I think he is looking for setting well below the voltage they are > set for. > > Another option would be to toss another pump into the bilge connected to the > other battery and just turn the battery switch off, but then we are looking > at a plumbing issue for a second overboard discharge. > > > Rich Gano > FROLIC 2005 Mainship 30 Pilot II > Panama City, FL > > > > > _______________________________________________ > http://lists.trawlering.com/mailman/listinfo/trawlers_lists.trawlering.com > > To unsubscribe or modify your subscription options (get password, change email address, etc) go to: http://lists.trawlering.com/mailman/listinfo/trawlers_lists.trawlering.com > Trawlers & Trawlering and T&T are trademarks of Water World > Productions. Unauthorized use is prohibited. > -- Peter Bennett, VE7CEI Vancouver, B.C., Canada Vancouver Power Squadron: http://vpsboat.org

If a battery is dying and the switch is on both, both batteries die; then the bilge starts to fill. You are correct about both discharging equally if the switch is on BOTH, as long as they are at the same capacity AND state of charge. But if one is weak, it will soon be discharged and take the good one with it. What he does not want to happen is to have his boat sink with a perfectly good, unaffected battery aboard which could have saved it. Rich Gano FROLIC 2005 Mainship 30 Pilot II Panama City, FL > It's not clear to me what he is trying to accomplish. > > If the battery switch is set to "both", both batteries will be discharged > equally, regardless of where the pump is physically connected. > > If the switch is set to "1", "2", or "Off", and the pump is connected directly to > one battery, only that battery will be discharged. The other battery will be > unaffected.