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I'm considering replacing my lead acid starting batteries on my boat with something like this. 500F @ 16v Starting battery module https://www.maxwell.com/images/documents/ESM_Manual_Install_4_15.pdf

I understand the high current risks associated with capacitors vs batteries. I had an older 12v 8d battery explode on the boat, my guess is that it was off gassing due to age and condition and the off gassing ignited.

I have seen what happens when a lead acid battery explodes, and the gas / acid is bad. What kind of gases/explosion/fire from a capacitor?

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  • \$\begingroup\$ so you your boat has no running lights or fixed radio? this is not a battery replacement \$\endgroup\$ – Jasen Apr 21 at 9:58
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It's pretty much the same, the explosion is faster because as soon as there is an internal short all the energy in the capacitor is dissipated into heat almost instantly. As far as gasses go, it depends on the electrolyte, and usually it's hydrogen. If the dielectric starts on fire, the smoke could be toxic.

Capacitors don't have near the storage capacity that batteries have and most capacitors leak current faster than batteries.

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  • \$\begingroup\$ Storage capacity is not relevant since all I need to do is start the engine. Charge time from dead to full is 15 or 30 minutes depending on model @ 25 Amps. So If my boat is at the dock for a month and I decide to leave I 30 minutes for engine checks and all the other "pre-flight" checks I don't see as a problem. Once Boating maintain the capacitors "charge" should be un-noticeable power draw. \$\endgroup\$ – SBTech Apr 19 at 21:31
  • \$\begingroup\$ 8D battery is 130lb of lead that needs replacing every 5 years, ESM Capacitor is 20lb and should never need replacing. In the event of an capacitor explosion its less mass, so less risk overall? \$\endgroup\$ – SBTech Apr 19 at 21:38

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