When charging, lead acid batteries generate hydrogen from the electrolysis of water, and some acid gases, the amount of which vary with the battery design, charging rate and state of charge. Hydrogen is explosive at concentrations above 4 percent and acid gases cause corrosion. This is why automobiles with batteries located under a seat or in the trunk are always vented outside through a vent tube. Some batteries designed for applications inside a vehicle are equipped with vent hose fittings, but most are not. Vehicle trunks are very poorly ventilated, and vehicle cabins are essentially unventilated when the vehicle is sitting still.
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Regarding the Quick-Fill wet cell battery fill system…I can recommend it without hesitation. Two years ago I was planning to replace all six of my 3+ year-old wet-cell batteries with AGM, but couldn’t overcome the $1,524 (+tax) total price delta and so I opted for new wet-cells and a $200 Flow-Rite Quick-Fill system (that Nigel Calder had highly recommended for significantly increasing the longevity of the batteries). As your article points out, the system allows me to remotely refill all battery cells to their recommended level without the time consuming hassle of removing all the boat’s mattresses, cushions and battery compartment access panels that [on my boat] have multiple screws. Moreover, no more removing each battery cap and dealing with ‘turkey baster bulb’ spills. Each month, I simply plug the system’s easily accessed filler hose into a bottle of distilled water and pump. The entire fill process for all the batteries now only takes <5 minutes rather than 60+ previously. One important note, according to FlowRite, the fill jug of distilled water must be located lower than the batteries when using the bulb pump…not sure why, but their tech support was adamant about this.
We had a scary event as we moved the boat to her winter berth north of Boston late October. After a calm motor sail into Boston and securing to the dock, we plugged in the shore line (first time in months as our boat is kept at her summer mooring). We settled in for a last sleep aboard of the season and were awoken to the CO detector in the aft cabin with no combustion sources active in or around the boat. Shortly after that alarm, a second CO detector sounded in the forward cabin. We evacuated the boat and summoned the fire department. They verified with their CO detectors that we had “over 228 ppm of CO” mostly near the bilge and over the 3 lead acid 8D batteries (5 year old) below the floors. After ventilating the boat and disconnecting the shore line, we started to unwind what happened.
Short answer, filling and testing the batteries are part of our winter prep checklist, but this event cause us to perform this right away! One single cell in one of the 8Ds was reading “low” by hydrometer, with the rest reading as “good”. Immediately an overcharge condition was suspected as the battery charger was trying to satisfy the current demand of the low battery at the expense of overcharging the other batteries. I was not able to verify the CO detectors used by the fire department were hydrogen compensated, but I suspect not since they were reading “CO” just like the ones installed in the boat.
Moral of the story- CO alarms from uncompensated detectors may be hydrogen outgassing, and test your battery frequently!
Everything is neat and tidy in the photo of the battery compartment at the beginning of this story except that the cable connections on the positive buss are not covered. Sure hate to drop a tool on there!