Lithium battery safety in a flooded ADCP

Ocean deployments of battery-powered instruments often include lithium battery packs, which enable deployments to last three times as long as they would using alkaline battery packs. Lithium batteries are widely regarded as hazardous. When we discovered that one of our ADCPs, which had been deployed with lithium batteries, had flooded, we worried whether the result would pose a risk. What we found was that while the ADCP´s electronics had irreparably corroded, the batteries had discharged but had not gotten particularly hot, and not much else had happened. This paper explains why things happen slowly in these lithium batteries, even when they are immersed in conductive sea water. The slow rate of discharge of these particular batteries prevents them from getting very hot in such circumstances. We conclude that these lithium batteries are probably not more dangerous than alkaline batteries, given appropriate venting of the pressure housing.