I use these without trouble
https://it.aliexpress.com/item/Connettore-LEMO-FVB-00-303-00B-LEMO-3-pin-Connettore-Per-wisycom-FVB-MTP40-MTP40S-MTP41/32836197001.html?spm=a2g0y.search0104.3.36.4ff87e5deqyiTt&ws_ab_test=searchweb0_0%2Csearchweb201602_4_10065_10068_10843_10059_10884_10887_10696_100031_10084_10083_10103_10618_10304_10307_10820_10821_10302%2Csearchweb201603_60%2CppcSwitch_0&algo_pvid=0ff58a9e-1d63-40fc-9123-2f51db56a304&priceBeautifyAB=0&algo_expid=0ff58a9e-1d63-40fc-9123-2f51db56a304-5
...may be this can help...
http://www.ebay.it/itm/Tamiya-AO-RC-Car-Parts-Antenna-Cap-Set-AO-5047-84189/371573756642?hash=item56838592e2:g:nI4AAOSwc-tY3mHx
...if you put a piece of plastic between two battery you open the chain... and you can leave the battery inside ready to be used if you loose the external energy.
In add you should cut the external power with a switcher, oterways the regulator remain in parallel at the battery and you can loose energy.